/*--------------------------------------------------------------------
 *
 *	Copyright (c) 1991-2024 by the GMT Team (https://www.generic-mapping-tools.org/team.html)
 *	See LICENSE.TXT file for copying and redistribution conditions.
 *
 *	This program is free software; you can redistribute it and/or modify
 *	it under the terms of the GNU Lesser General Public License as published by
 *	the Free Software Foundation; version 3 or any later version.
 *
 *	This program is distributed in the hope that it will be useful,
 *	but WITHOUT ANY WARRANTY; without even the implied warranty of
 *	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *	GNU Lesser General Public License for more details.
 *
 *	Contact info: www.generic-mapping-tools.org
 *--------------------------------------------------------------------*/
/*
 *  Misc statistical and special functions.
 *
 * Author:	Walter H. F. Smith, P. Wessel, R. Scharroo
 * Date:	1-JAN-2010
 * Version:	5.x
 *
 * A) List of exported gmt_* functions available to modules and libraries via gmt_dev.h:
 *
 *	gmt_Fcrit
 *	gmt_PvQv
 *	gmt_bei
 *	gmt_ber
 *	gmt_binom_cdf
 *	gmt_binom_pdf
 *	gmt_chebyshev
 *	gmt_chi2
 *	gmt_chi2_pdf
 *	gmt_chi2crit
 *	gmt_combination
 *	gmt_corrcoeff
 *	gmt_corrcoeff_f
 *	gmt_dilog
 *	gmt_erfinv
 *	gmt_extreme
 *	gmt_f_cdf
 *	gmt_f_pdf
 *	gmt_factorial
 *	gmt_fisher_pdf
 *	gmt_get_cellarea
 *	gmt_getmad
 *	gmt_getmad_f
 *	gmt_grd_lmsscl
 *	gmt_grd_mad
 *	gmt_grd_mean
 *	gmt_grd_median
 *	gmt_grd_mode
 *	gmt_grd_rms
 *	gmt_grd_std
 *	gmt_i0
 *	gmt_i1
 *	gmt_in
 *	gmt_k0
 *	gmt_k1
 *	gmt_kei
 *	gmt_ker
 *	gmt_kn
 *	gmt_lrand
 *	gmt_mean_and_std
 *	gmt_mean_weighted
 *	gmt_median
 *	gmt_median_weighted
 *	gmt_mode
 *	gmt_mode_f
 *	gmt_mode_weighted
 *	gmt_nrand
 *	gmt_permutation
 *	gmt_plm
 *	gmt_plm_bar
 *	gmt_plm_bar_all
 *	gmt_poisson_cdf
 *	gmt_poissonpdf
 *	gmt_psi
 *	gmt_quantile
 *	gmt_quantile_f
 *	gmt_quantile_weighted
 *	gmt_rand
 *	gmt_sig_f
 *	gmt_sinc
 *	gmt_std_weighted
 *	gmt_t_cdf
 *	gmt_t_pdf
 *	gmt_tcrit
 *	gmt_von_mises_mu_and_kappa
 *	gmt_vonmises_pdf
 *	gmt_weibull_cdf
 *	gmt_weibull_crit
 *	gmt_weibull_pdf
 *	gmt_zcrit
 *	gmt_zdist
 *
 * B) List of exported gmtlib_* functions available to libraries via gmt_internals.h:
 *
 *	gmtlib_compare_observation
 */

#include "gmt_dev.h"
#include "gmt_internals.h"

enum gmtstat_enum_cplx {GMT_RE = 0, GMT_IM = 1};	/* Real and imaginary indices */

/* --------- Local functions to this file ------- */

#define ITMAX 100

GMT_LOCAL double gmtstat_ln_gamma (struct GMT_CTRL *GMT, double xx) {
	/* Routine to compute natural log of Gamma(x)
		by Lanczos approximation.  Most accurate
		for x > 1; fails for x <= 0.  No error
		checking is done here; it is assumed
		that this is called by gmtstat_ln_gamma_r()  */

	static double cof[6] = {
		 76.18009173,
		-86.50532033,
		 24.01409822,
		 -1.231739516,
		0.120858003e-2,
		-0.536382e-5
	};

	double x, tmp, ser;

	int i;

	x = xx - 1.0;
	tmp = x + 5.5;
	tmp = (x + 0.5) * d_log (GMT,tmp) - tmp;
	ser = 1.0;
	for (i = 0; i < 6; i++) {
		x += 1.0;
		ser += (cof[i]/x);
	}
	return (tmp + d_log (GMT, 2.50662827465*ser) );
}

GMT_LOCAL int gmtstat_ln_gamma_r (struct GMT_CTRL *GMT, double x, double *lngam) {
	/* Get natural logarithm of Gamma(x), x > 0.
		To maintain full accuracy, this
		routine uses Gamma(1 + x) / x when
		x < 1.  This routine in turn calls
		gmtstat_ln_gamma(x), which computes the
		actual function value.  gmtstat_ln_gamma
		assumes it is being called in a
		smart way, and does not check the
		range of x.  */

	if (x > 1.0) {
		*lngam = gmtstat_ln_gamma (GMT, x);
		return (0);
	}
	if (x > 0.0 && x < 1.0) {
		*lngam = gmtstat_ln_gamma (GMT, 1.0 + x) - d_log (GMT,x);
		return (0);
	}
	if (x == 1.0) {
		*lngam = 0.0;
		return (0);
	}
	GMT_Report (GMT->parent, GMT_MSG_WARNING, "Ln Gamma:  Bad x (x <= 0).\n");
	return (GMT_NOTSET);
}

GMT_LOCAL void gmtstat_gamma_ser (struct GMT_CTRL *GMT, double *gamser, double a, double x, double *gln) {
	/* Returns the incomplete gamma function P(a,x) by series rep.
	 * Press et al, gser() */

	int n;
	double sum, del, ap;

	if (gmtstat_ln_gamma_r (GMT, a, gln) == GMT_NOTSET) {
		*gamser = GMT->session.d_NaN;
		return;
	}

	if (x < 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "x < 0 in gmtstat_gamma_ser(x)\n");
		*gamser = GMT->session.d_NaN;
		return;
	}
	if (x == 0.0) {
		*gamser = 0.0;
		return;
	}
	ap = a;
	del = sum = 1.0 / a;
	for (n = 1; n <= ITMAX; n++) {
	 	ap += 1.0;
	 	del *= x / ap;
	 	sum += del;
	 	if (fabs (del) < fabs (sum) * DBL_EPSILON) {
	 		*gamser = sum * exp (-x  + a * log (x) - (*gln));
	 		return;
	 	}
	}
	GMT_Report (GMT->parent, GMT_MSG_WARNING, "a too large, ITMAX too small in gmtstat_gamma_ser(x)\n");
}

GMT_LOCAL void gmtstat_gamma_cf (struct GMT_CTRL *GMT, double *gammcf, double a, double x, double *gln) {
	/* Returns the incomplete gamma function P(a,x) by continued fraction.
	 * Press et al, gcf() */
	int n;
	double gold = 0.0, g, fac = 1.0, b1 = 1.0;
	double b0 = 0.0, anf, ana, an, a1, a0 = 1.0;

	if (gmtstat_ln_gamma_r (GMT, a, gln) == GMT_NOTSET) {
		*gln = GMT->session.d_NaN;
		return;
	}

	a1 = x;
	for (n = 1; n <= ITMAX; n++) {
		an = (double) n;
		ana = an - a;
		a0 = (a1 + a0 * ana) * fac;
		b0 = (b1 + b0 * ana) * fac;
		anf = an * fac;
		a1 = x * a0 + anf * a1;
		b1 = x * b0 + anf * b1;
		if (a1 != 0.0) {
			fac = 1.0 / a1;
			g = b1 * fac;
			if (fabs ((g - gold) / g) < DBL_EPSILON) {
				*gammcf = exp (-x + a * log (x) - (*gln)) * g;
				return;
			}
			gold = g;
		}
	}
	GMT_Report (GMT->parent, GMT_MSG_WARNING, "a too large, ITMAX too small in gmtstat_gamma_cf(x)\n");
}

GMT_LOCAL double gmtstat_gammq (struct GMT_CTRL *GMT, double a, double x) {
	/* Returns Q(a,x) = 1 - P(a,x) Inc. Gamma function */

	double G = 0.0, gln;

	if (x < 0.0 || a <= 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "Invalid arguments to GMT_gammaq\n");
		return (GMT->session.d_NaN);
	}

	if (x < (a + 1.0)) {
		gmtstat_gamma_ser (GMT, &G, a, x, &gln);
		return (1.0 - G);
	}
	gmtstat_gamma_cf (GMT, &G, a, x, &gln);
	return (G);
}

#define BETA_EPS 3.0e-7

GMT_LOCAL double gmtstat_cf_beta (struct GMT_CTRL *GMT, double a, double b, double x) {
	/* Continued fraction method called by gmtstat_inc_beta.  */
	double am = 1.0, bm = 1.0, az = 1.0;
	double qab, qap, qam, bz, em, tem, d;
	double ap, bp, app, bpp, aold;

	int m = 0;

	qab = a + b;
	qap = a + 1.0;
	qam = a - 1.0;
	bz = 1.0 - qab * x / qap;

	do {
		m++;
		em = (double)m;
		tem = em + em;
		d = em*(b-m)*x/((qam+tem)*(a+tem));
		ap = az+d*am;
		bp = bz+d*bm;
		d = -(a+m)*(qab+em)*x/((a+tem)*(qap+tem));
		app = ap+d*az;
		bpp = bp+d*bz;
		aold = az;
		am = ap/bpp;
		bm = bp/bpp;
		az = app/bpp;
		bz = 1.0;
	} while (((fabs (az-aold) ) >= (BETA_EPS * fabs (az))) && (m < ITMAX));

	if (m == ITMAX) GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_cf_beta:  A or B too big, or ITMAX too small.\n");

	return (az);
}

GMT_LOCAL int gmtstat_inc_beta (struct GMT_CTRL *GMT, double a, double b, double x, double *ibeta) {
	double bt, gama, gamb, gamab;

	if (a <= 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_inc_beta:  Bad a (a <= 0).\n");
		return(GMT_NOTSET);
	}
	if (b <= 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_inc_beta:  Bad b (b <= 0).\n");
		return(GMT_NOTSET);
	}
	if (x > 0.0 && x < 1.0) {
		gmtstat_ln_gamma_r(GMT, a, &gama);
		gmtstat_ln_gamma_r(GMT, b, &gamb);
		gmtstat_ln_gamma_r(GMT, (a+b), &gamab);
		bt = exp(gamab - gama - gamb
			+ a * d_log (GMT, x) + b * d_log (GMT, 1.0 - x) );

		/* Here there is disagreement on the range of x which
			converges efficiently.  Abramowitz and Stegun
			say to use x < (a - 1) / (a + b - 2).  Editions
			of Numerical Recipes through mid 1987 say
			x < ( (a + 1) / (a + b + 1), but the code has
			x < ( (a + 1) / (a + b + 2).  Editions printed
			late 1987 and after say x < ( (a + 1) / (a + b + 2)
			in text as well as code.  What to do ? */

		if (x < ( (a + 1) / (a + b + 2) ) )
			*ibeta = bt * gmtstat_cf_beta (GMT, a, b, x) / a;
		else
			*ibeta = 1.0 - bt * gmtstat_cf_beta (GMT, b, a, (1.0 - x) ) / b;
		return(0);
	}
	else if (x == 0.0) {
		*ibeta = 0.0;
		return (0);
	}
	else if (x == 1.0) {
		*ibeta = 1.0;
		return (0);
	}
	else if (x < 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_inc_beta:  Bad x (x < 0).\n");
		*ibeta = 0.0;
	}
	else if (x > 1.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_inc_beta:  Bad x (x > 1).\n");
		*ibeta = 1.0;
	}
	return (GMT_NOTSET);
}

GMT_LOCAL int gmtstat_f_q (struct GMT_CTRL *GMT, double chisq1, uint64_t nu1, double chisq2, uint64_t nu2, double *prob) {
	/* Routine to compute Q(F, nu1, nu2) = 1 - P(F, nu1, nu2), where nu1
		and nu2 are positive integers, chisq1 and chisq2 are random
		variables having chi-square distributions with nu1 and nu2
		degrees of freedom, respectively (chisq1 and chisq2 >= 0.0),
		F = (chisq1/nu1)/(chisq2/nu2) has the F-distribution, and
		P(F, nu1, nu2) is the cumulative F-distribution, that is,
		the integral from 0 to (chisq1/nu1)/(chisq2/nu2) of the F-
		distribution.  Q = 1 - P is small when (chisq1/nu1)/(chisq2/nu2)
		is large with respect to 1.  That is, the value returned by
		this routine is the likelihood that an F >= (chisq1/nu1)/
		(chisq2/nu2) would occur by chance.

		Follows Abramowitz and Stegun.
		This is different from the method in Numerical Recipes, which
		uses the incomplete beta function but makes no use of the fact
		that nu1 and nu2 are known to be integers, and thus there is
		a finite limit on the sum for their expression.

		W H F Smith, August, 1999.

		REVISED by W H F Smith, October 27, 2000 after GMT 3.3.6 release.
		I found that the A&S methods overflowed for large nu1 and nu2, so
		I decided to go back to the gmtstat_inc_beta way of doing things.

	*/

	/* Check range of arguments:  */

	if (nu1 <= 0 || nu2 <= 0 || chisq1 < 0.0 || chisq2 < 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_f_q:  Bad argument(s).\n");
		return (GMT_NOTSET);
	}

	/* Extreme cases evaluate immediately:  */

	if (chisq1 == 0.0) {
		*prob = 1.0;
		return (0);
	}
	if (chisq2 == 0.0) {
		*prob = 0.0;
		return (0);
	}

	/* REVISION of Oct 27, 2000:  This inc beta call here returns
		the value.  All subsequent code is not used.  */

	if (gmtstat_inc_beta (GMT, 0.5*nu2, 0.5*nu1, chisq2/(chisq2+chisq1), prob) ) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_f_q:  Trouble in gmtstat_inc_beta call.\n");
		return (GMT_NOTSET);
	}
	return (0);
}

GMT_LOCAL int gmtstat_f_test_new (struct GMT_CTRL *GMT, double chisq1, uint64_t nu1, double chisq2, uint64_t nu2, double *prob, int iside) {
	/* Given chisq1 and chisq2, random variables distributed as chi-square
		with nu1 and nu2 degrees of freedom, respectively, except that
		chisq1 is scaled by var1, and chisq2 is scaled by var2, let
		the null hypothesis, H0, be that var1 = var2.  This routine
		assigns prob, the probability that we can reject H0 in favor
		of a new hypothesis, H1, according to iside:
			iside=+1 means H1 is that var1 > var2
			iside=-1 means H1 is that var1 < var2
			iside=0  means H1 is that var1 != var2.
		This routine differs from the old gmtstat_f_test() by adding the
		argument iside and allowing one to choose the test.  The old
		routine in effect always set iside=0.
		This routine also differs from gmtstat_f_test() in that the former
		used the incomplete beta function and this one uses gmtstat_f_q().

		Returns 0 on success, -1 on failure.

		WHF Smith, 12 August 1999.
	*/

	double q;	/* The probability from gmtstat_f_q(), which is the prob
				that H0 should be retained even though
				chisq1/nu1 > chisq2/nu2.  */

	if (chisq1 <= 0.0 || chisq2 <= 0.0 || nu1 < 1 || nu2 < 1) {
		*prob = GMT->session.d_NaN;
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_f_test_new: Bad argument(s).\n");
		return (GMT_NOTSET);
	}

	gmtstat_f_q (GMT, chisq1, nu1, chisq2, nu2, &q);

	if (iside > 0)
		*prob = 1.0 - q;
	else if (iside < 0)
		*prob = q;
	else if ((chisq1/nu1) <= (chisq2/nu2))
		*prob = 2.0*q;
	else
		*prob = 2.0*(1.0 - q);

	return (0);
}

GMT_LOCAL double gmtstat_factln (struct GMT_CTRL *GMT, int n) {
	/* returns log(n!) */
	static double a[101];	/* Automatically initialized to zero */
	if (n < 0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "n < 0 in gmtstat_factln(n)\n");
		return (GMT->session.d_NaN);
	}
	if (n <= 1) return 0.0;
	if (n <= 100) return (a[n] ? a[n] : (a[n] = gmtstat_ln_gamma (GMT, n+1.0)));
	else return gmtstat_ln_gamma (GMT, n+1.0);
}

GMT_LOCAL double gmtstat_beta (struct GMT_CTRL *GMT, double z, double w) {
	double g1 = 0.0, g2 = 0.0, g3 = 0.0;
	gmtstat_ln_gamma_r (GMT, z,   &g1);
	gmtstat_ln_gamma_r (GMT, w,   &g2);
	gmtstat_ln_gamma_r (GMT, z+w, &g3);
	return exp (g1 + g2 - g3);
}

#if 0 /* Legacy code */
GMT_LOCAL int gmtstat_f_test (struct GMT_CTRL *GMT, double chisq1, uint64_t nu1, double chisq2, uint64_t nu2, double *prob) {
	/* Routine to compute the probability that
		two variances are the same.
		chisq1 is distributed as chisq with
		nu1 degrees of freedom; ditto for
		chisq2 and nu2.  If these are independent
		and we form the ratio
		F = max(chisq1,chisq2)/min(chisq1,chisq2)
		then we can ask what is the probability
		that an F greater than this would occur
		by chance.  It is this probability that
		is returned in prob.  When prob is small,
		it is likely that the two chisq represent
		two different populations; the confidence
		that the two do not represent the same pop
		is 1.0 - prob.  This is a two-sided test.
	This follows some ideas in Numerical Recipes, CRC Handbook,
	and Abramowitz and Stegun.  */

	double f, df1, df2, p1, p2;

	if (chisq1 <= 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_ERROR, "gmtstat_f_test:  Chi-Square One <= 0.0\n");
		return(GMT_NOTSET);
	}
	if (chisq2 <= 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_ERROR, "gmtstat_f_test:  Chi-Square Two <= 0.0\n");
		return(GMT_NOTSET);
	}
	if (chisq1 > chisq2) {
		f = chisq1/chisq2;
		df1 = (double)nu1;
		df2 = (double)nu2;
	}
	else {
		f = chisq2/chisq1;
		df1 = (double)nu2;
		df2 = (double)nu1;
	}
	if (gmtstat_inc_beta(GMT, 0.5*df2, 0.5*df1, df2/(df2+df1*f), &p1) ) {
		GMT_Report (GMT->parent, GMT_MSG_ERROR, "gmtstat_f_test:  Trouble on 1st gmtstat_inc_beta call.\n");
		return(GMT_NOTSET);
	}
	if (gmtstat_inc_beta(GMT, 0.5*df1, 0.5*df2, df1/(df1+df2/f), &p2) ) {
		GMT_Report (GMT->parent, GMT_MSG_ERROR, "gmtstat_f_test:  Trouble on 2nd gmtstat_inc_beta call.\n");
		return(GMT_NOTSET);
	}
	*prob = p1 + (1.0 - p2);
	return (0);
}
#endif

GMT_LOCAL int gmtstat_student_t_a (struct GMT_CTRL *GMT, double t, uint64_t n, double *prob) {
	/* Probability integral called A(t,n) by Abramowitz &
	Stegun for the student's t distribution with n degrees
	of freedom.  Uses expressions A&S 26.7.3 and 26.7.4

	If X is distributed N(0,1) and V is distributed chi-
	square with n degrees of freedom, then
	tau = X / sqrt(V/n) is said to have Student's t-
	distribution with n degrees of freedom.  For example,
	tau could be the sample mean divided by the sample
	standard deviation, for a sample of N points; then
	n = N - 1.

	This function sets *prob = GMT->session.d_NaN and returns (-1)
	if t < 0.  Otherwise it sets *prob = the probability
	fabs(tau) <= t and returns (0).

	As n -> oo, we can replace this function with
	erf (t / M_SQRT2).  However, it isn't clear how large
	n has to be to make this a good approximation.  I
	consulted six books; one of them suggested this
	approximation for n >= 30, but all the others did not
	say when to use this approximation (A&S, in particular,
	does not say).  I tried some numerical experiments
	which suggested that the relative error in this
	approximation would be < 0.01 for n > 30, all t, but
	I also found that the expression here is stable to
	large n and large t, so I decided to leave it as is.

	W H F Smith, August 1999.
*/

	double	theta, s, c, csq, term, sum;
	int64_t	k, kstop, kt, kb;

	if (t < 0.0 || n == 0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmtstat_student_t_a:  Bad argument(s).\n");
		*prob = GMT->session.d_NaN;
		return (GMT_NOTSET);
	}

	if (t == 0.0) {
		*prob = 0.0;
		return (0);
	}

	theta = atan (t/sqrt ((double)n));

	if (n == 1) {
		*prob = 2.0 * theta / M_PI;
		return (0);
	}

	sincos (theta, &s, &c);

	csq = c * c;

	kstop = n-2;
	if (n%2 == 1) {
		kt = 0;
		kb = 1;
		k = 1;
		term = c;
	}
	else {
		kt = -1;
		kb = 0;
		k = 0;
		term = 1.0;
	}
	sum = term;
	while (k < kstop) {
		k += 2;
		kt += 2;
		kb += 2;
		term *= (kt * csq)/kb;
		sum += term;
	}

	sum *= s;

	if (n%2 == 1)
		*prob = 2.0 * (theta + sum) / M_PI;
	else
		*prob = sum;

	/* Adjust in case of roundoff:  */

	if (*prob < 0.0) *prob = 0.0;
	if (*prob > 1.0) *prob = 1.0;

	return (0);
}

GMT_LOCAL void gmtstat_Cmul (double A[], double B[], double C[]) {
	/* Complex multiplication */
	C[GMT_RE] = A[GMT_RE]*B[GMT_RE] - A[GMT_IM]*B[GMT_IM];
	C[GMT_IM] = A[GMT_RE]*B[GMT_IM] + A[GMT_IM]*B[GMT_RE];
}

GMT_LOCAL void gmtstat_Cdiv (double A[], double B[], double C[]) {
	/* Complex division */
	double denom;
	denom = B[GMT_RE]*B[GMT_RE] + B[GMT_IM]*B[GMT_IM];
	C[GMT_RE] = (A[GMT_RE]*B[GMT_RE] + A[GMT_IM]*B[GMT_IM])/denom;
	C[GMT_IM] = (A[GMT_IM]*B[GMT_RE] - A[GMT_RE]*B[GMT_IM])/denom;
}

#if 0	/* Unused */
GMT_LOCAL void gmtstat_Ccot (double Z[], double cotZ[]) {
	/* Complex cot(z) */
	double sx, cx, e, A[2], B[2];

	sincos (2.0*Z[0], &sx, &cx);
	e = exp (-2.0*Z[1]);
	A[0] = -e * sx;		A[1] = B[0] = e * cx;
	A[1] += 1.0;	B[0] -= 1.0;	B[1] = -A[0];
	gmtstat_Cdiv (A, B, cotZ);
}
#endif

GMT_LOCAL double gmtstat_Cabs (double A[]) {
	return (hypot (A[GMT_RE], A[GMT_IM]));
}

GMT_LOCAL void gmtstat_F_to_ch1_ch2 (struct GMT_CTRL *GMT, double F, double nu1, double nu2, double *chisq1, double *chisq2) {
	/* Silly routine to break F up into parts needed for gmtstat_f_q */
	gmt_M_unused(GMT);
	*chisq2 = 1.0;
	*chisq1 = F * nu1 / nu2;
}

int gmtlib_compare_observation (const void *a, const void *b) {
	const struct GMT_OBSERVATION *obs_1 = a, *obs_2 = b;

	/* Sorts observations into ascending order based on obs->value */
	if (obs_1->value < obs_2->value)
		return -1;
	if (obs_1->value > obs_2->value)
		return 1;
	return 0;
}

int gmt_sig_f (struct GMT_CTRL *GMT, double chi1, uint64_t n1, double chi2, uint64_t n2, double level, double *prob) {
	/* Returns true if chi1/n1 significantly less than chi2/n2
		at the level level.  Returns false if:
			error occurs in gmtstat_f_test_new();
			chi1/n1 not significantly < chi2/n2 at level.

			Changed 12 August 1999 to use gmtstat_f_test_new()  */

	int trouble;

	trouble = gmtstat_f_test_new (GMT, chi1, n1, chi2, n2, prob, -1);
	if (trouble) return (0);
	return ((*prob) >= level);
}

/*
 * Kelvin-Bessel functions, ber, bei, ker, kei.  ber(x) and bei(x) are even;
 * ker(x) and kei(x) are defined only for x > 0 and x >=0, respectively.
 * For x <= 8 we use polynomial approximations in Abramowitz & Stegun.
 * For x > 8 we use asymptotic series of Russell, quoted in Watson (Theory
 * of Bessel Functions).
 */

double gmt_ber (struct GMT_CTRL *GMT, double x) {
	double t, rxsq, alpha, beta;
	gmt_M_unused(GMT);

	if (x == 0.0) return (1.0);

	/* ber is an even function of x:  */
	x = fabs (x);

	if (x <= 8.0) {
		/* Telescoped power series from Abramowitz & Stegun  */
		t = x * 0.125;
		t *= t;
		t *= t;	/* t = pow(x/8, 4)  */
		return (1.0 + t*(-64.0 + t*(113.77777774 + t*(-32.36345652 + t*(2.64191397 + t*(-0.08349609 + t*(0.00122552 - 0.00000901 * t)))))));
	}
	else {
		/* Russell's asymptotic approximation, from Watson, p. 204  */

		rxsq = 1.0 / (x * x);
		t = x / M_SQRT2;

		alpha = t;
		beta  = t - 0.125 * M_PI;
		t *= 0.125 * rxsq;
		alpha += t;
		beta  -= t;
		beta  -= 0.0625*rxsq;
		t *= (25.0/48.0)*rxsq;
		alpha -= t;
		beta  -= t;
		alpha -= (13.0/128.0)*(rxsq*rxsq);

		return (exp (alpha) * cos (beta) / sqrt (2.0 * M_PI * x) );
	}
}

double gmt_bei (struct GMT_CTRL *GMT, double x) {
	double t, rxsq, alpha, beta;
	gmt_M_unused(GMT);

	if (x == 0.0) return (0.0);

	/* bei is an even function of x:  */
	x = fabs(x);

	if (x <= 8.0) {
		/* Telescoped power series from Abramowitz & Stegun  */
		t = x * 0.125;
		rxsq = t*t;
		t = rxsq * rxsq;	/* t = pow(x/8, 4)  */
		return (rxsq * (16.0 + t*(-113.77777774 + t*(72.81777742 + t*(-10.56765779 + t*(0.52185615 + t*(-0.01103667 + t*(0.00011346))))))));
	}
	else {
		/* Russell's asymptotic approximation, from Watson, p. 204  */

		rxsq = 1.0 / (x * x);
		t = x / M_SQRT2;

		alpha = t;
		beta  = t - 0.125 * M_PI;
		t *= 0.125 * rxsq;
		alpha += t;
		beta  -= t;
		beta  -= 0.0625*rxsq;
		t *= (25.0/48.0)*rxsq;
		alpha -= t;
		beta  -= t;
		alpha -= (13.0/128.0)*(rxsq*rxsq);

		return (exp (alpha) * sin (beta) / sqrt (2.0 * M_PI * x));
	}
}

double gmt_ker (struct GMT_CTRL *GMT, double x) {
	double t, rxsq, alpha, beta;

	if (x <= 0.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "x <= 0 in gmt_ker(x)\n");
		return (GMT->session.d_NaN);
	}

	if (x <= 8.0) {
		/* Telescoped power series from Abramowitz & Stegun  */
		t = 0.125 * x;
		t *= t;
		t *= t;  /* t = pow(x/8, 4)  */
		return (-log (0.5 * x) * gmt_ber (GMT, x) + 0.25 * M_PI * gmt_bei (GMT, x) -M_EULER + \
			t * (-59.05819744 + t * (171.36272133 + t * (-60.60977451 + t * (5.65539121 + t * (-0.199636347 + t * (0.00309699 + t * (-0.00002458 * t))))))));
	}
	else {
		/* Russell's asymptotic approximation, from Watson, p. 204  */

		rxsq = 1.0 / (x * x);
		t = -x / M_SQRT2;

		alpha = t;
		beta  = t - 0.125 * M_PI;
		t *= 0.125 * rxsq;
		alpha += t;
		beta  -= t;
		beta  -= 0.0625*rxsq;
		t *= (25.0/48.0)*rxsq;
		alpha -= t;
		beta  -= t;
		alpha -= (13.0/128.0)*(rxsq*rxsq);

		return (exp (alpha) * cos (beta) / sqrt (2.0 * x / M_PI));
	}
}

double gmt_kei (struct GMT_CTRL *GMT, double x) {
	double t, rxsq, alpha, beta;

	if (x <= 0.0) {
		/* Zero is valid.  If near enough to zero, return kei(0)  */
		if (x > -GMT_CONV8_LIMIT) return (-0.25 * M_PI);

		GMT_Report (GMT->parent, GMT_MSG_WARNING, "x < 0 in gmt_kei(x)\n");
		return (GMT->session.d_NaN);
	}

	if (x <= 8.0) {
		/* Telescoped power series from Abramowitz & Stegun  */
		t = x * 0.125;
		rxsq = t*t;
		t = rxsq * rxsq;	/* t = pow(x/8, 4)  */
		return (-log (0.5 * x) * gmt_bei (GMT, x) - 0.25 * M_PI * gmt_ber (GMT, x) +
			rxsq * (6.76454936 + t * (-142.91827687 + t * (124.23569650 + t * (-21.30060904 + t * (1.17509064 + t * (-0.02695875 + t * (0.00029532 * t))))))));
	}
	else {
		/* Russell's asymptotic approximation, from Watson, p. 204  */

		rxsq = 1.0 / (x * x);
		t = -x / M_SQRT2;

		alpha = t;
		beta  = t - 0.125 * M_PI;
		t *= 0.125 * rxsq;
		alpha += t;
		beta  -= t;
		beta  -= 0.0625*rxsq;
		t *= (25.0/48.0)*rxsq;
		alpha -= t;
		beta  -= t;
		alpha -= (13.0/128.0)*(rxsq*rxsq);

		return (exp (alpha) * sin (beta) / sqrt (2.0 * x / M_PI));
	}
}

double gmt_i0 (struct GMT_CTRL *GMT, double x) {
/* Modified from code in Press et al. */
	double y, res;
	gmt_M_unused(GMT);

	if (x < 0.0) x = -x;

	if (x < 3.75) {
		y = x * x / 14.0625;
		res = 1.0 + y * (3.5156229 + y * (3.0899424 + y * (1.2067492 + y * (0.2659732 + y * (0.360768e-1 + y * 0.45813e-2)))));
	}
	else {
		y = 3.75 / x;
		res = (exp (x) / sqrt (x)) * (0.39894228 + y * (0.1328592e-1 + y * (0.225319e-2 + y * (-0.157565e-2 + y * (0.916281e-2 + y * (-0.2057706e-1 + y * (0.2635537e-1 + y * (-0.1647633e-1 + y * 0.392377e-2))))))));
	}
	return (res);
}

double gmt_i1 (struct GMT_CTRL *GMT, double x) {
	/* Modified Bessel function I1(x) */
	double y, res;
	gmt_M_unused(GMT);

	if (x < 0.0) x = -x;
	if (x < 3.75) {
		y = pow (x / 3.75, 2.0);
		res = x * (0.5 + y * (0.87890594 + y * (0.51498869 + y * (0.15084934 + y * (0.02658733 + y * (0.00301532 + y * 0.00032411))))));
	}
	else {
		y = 3.75 / x;
		res = (exp (x) / sqrt (x)) * (0.39894228 + y * (-0.03988024 + y * (-0.00362018 + y * (0.00163801+ y * (-0.01031555 + y * (0.02282967 + y * (-0.02895312 + y * (0.01787654 -y * 0.00420059))))))));
		if (x < 0.0) res = - res;
	}
	return (res);
}

double gmt_in (struct GMT_CTRL *GMT, unsigned int n, double x) {
	/* Modified Bessel function In(x) */

	unsigned int j, m, IACC = 40;
	double res, tox, bip, bi, bim;
	double BIGNO = 1.0e10, BIGNI = 1.0e-10;

	if (n == 0) return (gmt_i0 (GMT, x));
	if (n == 1) return (gmt_i1 (GMT, x));
	if (x == 0.0) return (0.0);

	tox = 2.0 / fabs (x);
	bip = res = 0.0;
	bi = 1.0;
	m = 2 * (n + urint (sqrt ((double)(IACC * n))));
	for (j = m; j >= 1; j--) {
		bim = bip + ((double)j) * tox * bi;
		bip = bi;
		bi = bim;
		if (fabs (bi) > BIGNO) {
			res *= BIGNI;
			bi *= BIGNI;
			bip *= BIGNI;
		}
		if (j == n) res = bip;
	}
	res *= (gmt_i0 (GMT, x) / bi);
	if (x < 0.0 && (n%2)) res = -res;

	return (res);
}

double gmt_k0 (struct GMT_CTRL *GMT, double x) {
/* Modified from code in Press et al. */
	double y, z, res;
	gmt_M_unused(GMT);

	if (x < 0.0) x = -x;

	if (x <= 2.0) {
		y = 0.25 * x * x;
		z = x * x / 14.0625;
		res = (-log(0.5*x) * (1.0 + z * (3.5156229 + z * (3.0899424 + z * (1.2067492 + z * (0.2659732 + z * (0.360768e-1 + z * 0.45813e-2))))))) + (-M_EULER + y * (0.42278420 + y * (0.23069756 + y * (0.3488590e-1 + y * (0.262698e-2 + y * (0.10750e-3 + y * 0.74e-5))))));
	}
	else {
		y = 2.0 / x;
		res = (exp (-x) / sqrt (x)) * (1.25331414 + y * (-0.7832358e-1 + y * (0.2189568e-1 + y * (-0.1062446e-1 + y * (0.587872e-2 + y * (-0.251540e-2 + y * 0.53208e-3))))));
	}
	return (res);
}

double gmt_k1 (struct GMT_CTRL *GMT, double x) {
	/* Modified Bessel function K1(x) */

	double y, res;

	if (x < 0.0) x = -x;
	if (x <= 2.0) {
		y = x * x / 4.0;
		res = (log (0.5 * x) * gmt_i1 (GMT, x)) + (1.0 / x) * (1.0 + y * (0.15443144 + y * (-0.67278579 + y * (-0.18156897 + y * (-0.01919402 + y * (-0.00110404 - y * 0.00004686))))));
	}
	else {
		y = 2.0 / x;
		res = (exp (-x) / sqrt (x)) * (1.25331414 + y * (0.23498619 + y * (-0.03655620 + y * (0.01504268 + y * (-0.00780353 + y * (0.00325614 - y * 0.00068245))))));
	}
	return (res);
}

double gmt_kn (struct GMT_CTRL *GMT, unsigned int n, double x) {
	/* Modified Bessel function Kn(x) */

	unsigned int j;
	double bkm, bk, bkp, tox;

	if (n == 0) return (gmt_k0 (GMT, x));
	if (n == 1) return (gmt_k1 (GMT, x));

	tox = 2.0 / x;
	bkm = gmt_k0 (GMT, x);
	bk = gmt_k1 (GMT, x);
	for (j = 1; j <= (n-1); j++) {
		bkp = bkm + j * tox * bk;
		bkm = bk;
		bk = bkp;
	}

	return (bk);
}

double gmt_plm (struct GMT_CTRL *GMT, int l, int m, double x) {
	/* Unnormalized associated Legendre polynomial of degree l and order m, including
	 * Condon-Shortley phase (-1)^m */
	double fact, pll = 0, pmm, pmmp1, somx2;
	int i, ll;

	/* x is cosine of colatitude and must be -1 <= x <= +1 */
	if (fabs(x) > 1.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "|x| > 1.0 in gmt_plm\n");
		return (GMT->session.d_NaN);
	}

	if (m < 0 || m > l) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmt_plm requires 0 <= m <= l.\n");
		return (GMT->session.d_NaN);
	}

	pmm = 1.0;
	if (m > 0) {
		somx2 = d_sqrt ((1.0 - x) * (1.0 + x));
		fact = 1.0;
		/* This loop used to go to i < m; corrected to i <= m by WHFS  */
		for (i = 1; i <= m; i++) {
			pmm *= -fact * somx2;
			fact += 2.0;
		}
	}
	if (l == m) return (pmm);

	pmmp1 = x * (2*m + 1) * pmm;
	if (l == (m + 1)) return (pmmp1);

	for (ll = (m+2); ll <= l; ll++) {
		pll = (x * (2*ll - 1) * pmmp1 - (ll + m - 1) * pmm) / (ll - m);
		pmm = pmmp1;
		pmmp1 = pll;
	}
	return (pll);
}

#ifndef M_SQRTPI
#define M_SQRTPI	1.77245385090551602729	
#endif

double gmt_plm_bar (struct GMT_CTRL *GMT, int l, int m, double x, bool ortho) {
	/* This function computes the normalized associated Legendre function of x for degree
	 * l and order m. x must be in the range [-1;1] and 0 <= |m| <= l.
	 * The routine is largely based on the second modified forward column method described in
	 * Holmes and Featherstone (2002). It is stable up to very high degree and order
	 * (at least 3000). This is achieved by individually computing the sectorials to P_m,m
	 * and then iterate up to P_l,m divided by P_m,m and the scale factor 1e280.
	 * Eventually, the result is multiplied again with these two terms.
	 *
	 * When ortho=false, normalization is according to the geophysical convention.
	 * - The Condon-Shortley phase (-1)^m is NOT included.
	 * - The normalization factor is sqrt(k*(2l+1)*(l-m)!/(l+m)!) with k=2 except for m=0: k=1.
	 * - The integral of Plm**2 over [-1;1] is 2*k.
	 * - The integrals of (Plm*cos(m*lon))**2 and (Plm*sin(m*lon))**2 over a sphere are 4 pi.
	 *
	 * When ortho=true, the results are orthonormalized.
	 * - The Condon-Shortley phase (-1)^m is NOT included.
	 * - The normalization factor is sqrt((2l+1)*(l-m)!/(l+m)!/(4*pi)).
	 * - The integral of Plm**2 over [-1;1] is 1/(2*pi).
	 * - The integral of (Plm*exp(i*m*lon))**2 over a sphere is 1.
	 *
	 * When called with -m, the Condon-Shortley phase will be included.
	 *
	 * Note that the orthonormalized form produces an integral of 1 when using imaginary terms
	 * for longitude. In geophysics, the imaginary components are split into cosine and sine terms
	 * EACH of which have an average power of 1 over the sphere (i.e. an integral of 4 pi).
	 *
	 * This routine could be further expanded to produce an array of P_m,m through P_l,m. This
	 * would be practical if Legendre functions of various degrees are to be computed at the same
	 * latitude. Also, differentials could be added.
	 *
	 * Reference:
	 * S. A. Holmes and W. E. Featherstone. A unified approach to the Clenshaw summation and the
	 * recursive computation of very high degree and order normalised associated Legendre functions.
	 * Journal of Geodesy, 76, 279-299, 2002. doi:10.1007/s00190-002-0216-2.
	 */
	int i;
	bool csphase = false;
	double scalef = 1.0e280, u, r, pmm, pmm0, pmm1, pmm2;

	/* x is cosine of colatitude (sine of latitude) and must be -1 <= x <= +1 */

	if (fabs (x) > 1.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "|x| > 1.0 in gmt_plm_bar\n");
		return (GMT->session.d_NaN);
	}

	/* If m is negative, include Condon-Shortley phase */

	if (m < 0) {
		csphase = true;
		m = -m;
	}

	if (m > l) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmt_plm_bar requires 0 <= m <= l.\n");
		return (GMT->session.d_NaN);
	}

	/* u is sine of colatitude (cosine of latitude) so that 0 <= s <= 1 */

	u = d_sqrt ((1.0 - x)*(1.0 + x));

	/* Initialize P_00 = 1 and compute up to P_mm using recurrence relation.
	   The result is a normalisation factor: sqrt((2l+1)(l-m)!/(l+m)!) */

	pmm = 1.0;
	for (i = 1; i <= m; i++) pmm = d_sqrt (1.0 + 0.5/i) * u * pmm;

	/* If orthonormalization is requested: multiply by sqrt(1/4pi)
	   In case of geophysical conversion : multiply by sqrt(2-delta_0m) */

	if (ortho)
		pmm /= (M_SQRT2 * M_SQRTPI);
	else if (m != 0)
		pmm *= M_SQRT2;

	/* If C-S phase is requested, apply it now */

	if ((m & 1) && csphase) pmm = -pmm;

	/* If l==m, we are done */

	if (l == m) return (pmm);

	/* In the next section all P_l,m are divided by (P_m,m * scalef).
	   First compute P_m+1,m / P_m,m */

	pmm0 = 1.0/scalef;
	pmm1 = pmm0 * x * d_sqrt ((double)(2*m + 3));

	/* Use second modified column forward recurrence relation to compute P_m+2,m / P_m,m */

	for (i = m+2; i <= l; i++) {
		r = (2*i+1.0) / (i+m) / (i-m);
		pmm2 = x * pmm1 * d_sqrt(r*(2*i-1)) - pmm0 * d_sqrt(r*(i-m-1)*(i+m-1)/(2*i-3));
		pmm0 = pmm1;
		pmm1 = pmm2;
	}

	/* Return P_l,m */

	pmm1 *= pmm;
	pmm1 *= scalef;
	return (pmm1);
}

void gmt_plm_bar_all (struct GMT_CTRL *GMT, int lmax, double x, bool ortho, double *plm) {
	/* This function computes the normalized associated Legendre function of x for all degrees
	 * l <= lmax and all orders m <= l. x must be in the range [-1;1] and 0 <= |m| <= l.
	 * The routine is largely based on the second modified forward column method described in
	 * Holmes and Featherstone (2002). It is stable up to very high degree and order
	 * (at least 3000). This is achieved by individually computing the sectorials to P_m,m
	 * and then iterate up to P_l,m divided by P_m,m and the scale factor 1e280.
	 * Eventually, the result is multiplied again with these two terms.
	 *
	 * When ortho=false, normalization is according to the geophysical convention.
	 * - The Condon-Shortley phase (-1)^m is NOT included.
	 * - The normalization factor is sqrt(k*(2l+1)*(l-m)!/(l+m)!) with k=2 except for m=0: k=1.
	 * - The integral of Plm**2 over [-1;1] is 2*k.
	 * - The integrals of (Plm*cos(m*lon))**2 and (Plm*sin(m*lon))**2 over a sphere are 4 pi.
	 *
	 * When ortho=true, the results are orthonormalized.
	 * - The Condon-Shortley phase (-1)^m is NOT included.
	 * - The normalization factor is sqrt((2l+1)*(l-m)!/(l+m)!/(4*pi)).
	 * - The integral of Plm**2 over [-1;1] is 1/(2*pi).
	 * - The integral of (Plm*exp(i*m*lon))**2 over a sphere is 1.
	 *
	 * When called with -lmax, the Condon-Shortley phase will be included.
	 *
	 * Note that the orthonormalized form produces an integral of 1 when using imaginary terms
	 * for longitude. In geophysics, the imaginary components are split into cosine and sine terms
	 * EACH of which have an average power of 1 over the sphere (i.e. an integral of 4 pi).
	 *
	 * This routine produces an array of all values of P_l,m(x) in the array plm, in the order
	 * P_0,0 P_1,0 P_1,1 P_2,0 P_2,1 P_2,2, etc. That means that plm[j] refers to:
	 * tesserals  P_l,m  when  j = l * (l+1) / 2 + m
	 * zonals     P_l,0  when  j = l * (l+1) / 2
	 * sectorials P_m,m  when  j = m * (m+3) / 2
	 *
	 * Reference:
	 * S. A. Holmes and W. E. Featherstone. A unified approach to the Clenshaw summation and the
	 * recursive computation of very high degree and order normalised associated Legendre functions.
	 * Journal of Geodesy, 76, 279-299, 2002. doi:10.1007/s00190-002-0216-2.
	 */
	int l, m, lm, mm;
	bool csphase = false;
	double scalef = 1.0e280, u, r, pmm, pmms, pmm0, pmm1, pmm2;

	/* x is cosine of colatitude (sine of latitude) and must be -1 <= x <= +1 */

	if (fabs (x) > 1.0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "|x| > 1.0 in gmt_plm_bar_all\n");
		return;
	}

	/* If lmax is negative, include Condon-Shortley phase */

	if (lmax < 0) {
		csphase = true;
		lmax = -lmax;
	}

	/* u is sine of colatitude (cosine of latitude) so that 0 <= s <= 1 */

	u = d_sqrt ((1.0 - x)*(1.0 + x));

	/* Initialize P_00 = 1 */
	mm = 0;
	plm[mm] = pmm = 1.0;

	/* Loop over 0 <= m <= lmax */

	for (m = 0; m <= lmax; m++, mm += m+1) {

		/* Compute up P_mm using recurrence relation.
		The result is a normalisation factor: sqrt((2l+1)(l-m)!/(l+m)!) */

		if (m != 0) pmm *= d_sqrt (1.0 + 0.5/m) * u;

		/* If orthonormalization is requested: multiply by sqrt(1/4pi)
		In case of geophysical conversion : multiply by sqrt(2-delta_0m) */

		if (ortho)
			plm[mm] = pmm / (M_SQRT2 * M_SQRTPI);
		else if (m != 0)
			plm[mm] = pmm * M_SQRT2;

		/* If C-S phase is requested, apply it now */

		if ((m & 1) && csphase) plm[mm] = -plm[mm];

		/* In the next section all P_l,m are divided by (P_m,m * scalef).
		First compute P_m+1,m / P_m,m */

		pmms = plm[mm] * scalef;
		pmm0 = 1.0 / scalef;
		pmm1 = pmm0 * x * d_sqrt ((double)(2*m + 3));
		lm = mm + m + 1;
		plm[lm] = pmm1 * pmms;

		/* Use second modified column forward recurrence relation to compute P_m+2,m / P_m,m */

		for (l = m+2; l <= lmax; l++) {
			r = (2*l+1.0) / (l+m) / (l-m);
			pmm2 = x * pmm1 * d_sqrt(r*(2*l-1)) - pmm0 * d_sqrt(r*(l-m-1)*(l+m-1)/(2*l-3));
			pmm0 = pmm1;
			pmm1 = pmm2;
			lm += l;
			plm[lm] = pmm1 * pmms;
		}
	}
}

/* gmt_sinc (x) calculates the sinc function */

double gmt_sinc (struct GMT_CTRL *GMT, double x) {
	gmt_M_unused(GMT);
	if (x == 0.0) return (1.0);
	x *= M_PI;
	return (sin (x) / x);
}

/* gmt_factorial (n) calculates the factorial n! */

double gmt_factorial (struct GMT_CTRL *GMT, int n) {
	static int ntop = 10;	/* Initial portion filled in below */
	static double a[33] = {1.0, 1.0, 2.0, 6.0, 24.0, 120.0, 720.0, 5040.0, 40320.0, 362880.0, 3628800.0};
	int i;

	if (n < 0) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "n < 0 in gmt_factorial(n)\n");
		return (GMT->session.d_NaN);
		/* This could be set to return 0 without warning, to facilitate
			sums over binomial coefficients, if desired.  -whfs  */
	}
	if (n > 32) return (exp(gmtstat_ln_gamma (GMT, n+1.0)));
	while (ntop < n) {
		i = ntop++;
		a[ntop] = a[i] * ntop;
	}
	return (a[n]);
}

double gmt_permutation (struct GMT_CTRL *GMT, int n, int r) {
	/* Compute Permutations n_P_r */
	if (n < 0 || r < 0 || r > n) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "n < 0 or r < 0 or r > n in gmt_permutation(n,r)\n");
		return (GMT->session.d_NaN);
	}
	return (floor (0.5 + exp (gmtstat_factln (GMT, n) - gmtstat_factln (GMT, n-r))));
}

double gmt_combination (struct GMT_CTRL *GMT, int n, int r) {
	/* Compute Combinations n_C_r */
	if (n < 0 || r < 0 || r > n) {
		GMT_Report (GMT->parent, GMT_MSG_WARNING, "n < 0 or r < 0 or r > n in gmt_combination(n,r)\n");
		return (GMT->session.d_NaN);
	}
	return (floor (0.5 + exp (gmtstat_factln (GMT, n) - gmtstat_factln (GMT, r) - gmtstat_factln (GMT, n-r))));
}

double gmt_dilog (struct GMT_CTRL *GMT, double x) {
	/* Compute dilog(x) (defined for x >= 0) by the method of Parker's
	   Appendix A of his Geophysical Inverse Theory.  The function
	   is needed for x in the range 0 <= x <= 1 when solving the
	   spherical spline interpolation in section 2.07 of Parker.

	   I tested this for x in range 0 to 1 by reproducing Figure
	   2.07c of Parker's book.  I also tested that the result was
	   smooth for x out to 25.  I also checked d[dilog(x)]/dx
	   obtained numerically from this routine against an analytic
	   expression, and I found the smallest angular separation
	   between two points on a sphere such that their Gram
	   matrix expression (see Parker) was different from 1; this
	   is smallest epsilon such that dilog(epsilon) - dilog(0)
	   != 0.0.  This turned out to be very much smaller than I
	   would have guessed from the apparent e-15 accuracy of
	   Parker's polynomial.  So I think this is very accurate.

	   If this is called with x < 0, it returns dilog(0) and
	   prints a warning.  It could also be set to return NaN.
	   I did this because in applications it might happen that
	   an x which should be zero is computed to be slightly off,
	   in which case the desired result is for x = 0.

	   23 Oct 1996 WHFS.   */

	double pisqon6, y, ysq, z;

	if (x < -GMT_CONV8_LIMIT) return (GMT->session.d_NaN);	/* Tolerate minor slop before we are outside domain */

	pisqon6 = M_PI * M_PI / 6.0;
	if (x <= 0.0) return (pisqon6);	/* Meaning -GMT_CONV8_LIMIT < x <= 0 */

	if (x < 0.5) {
		y = -log (1.0 - x);
		ysq = y * y;
		z = y * (1.0 + y * (-0.25 + y * (0.027777777777213 + ysq * (-2.7777776990e-04 + ysq * (4.724071696e-06 + ysq * (-9.1764954e-08 + 1.798670e-09 * ysq))))));
		return (pisqon6 - z + y * log (x));
	}
	if (x < 2.0) {
		y = -log (x);
		ysq = y * y;
		z = y * (1.0 + y * (-0.25 + y * (0.027777777777213 + ysq * (-2.7777776990e-04 + ysq * (4.724071696e-06 + ysq * (-9.1764954e-08 + 1.798670e-09 * ysq))))));
		return (z);
	}
	y = log (x);
	ysq = y * y;
	z = y * (1.0 + y * (-0.25 + y * (0.027777777777213 + ysq * (-2.7777776990e-04 + ysq * (4.724071696e-06 + ysq * (-9.1764954e-08 + 1.798670e-09 * ysq))))));
	return (-z - 0.5 * ysq);
}

#ifndef M_2_SQRTPI
#define  M_2_SQRTPI      1.12837916709551257390
#endif

double gmt_erfinv (struct GMT_CTRL *GMT, double y) {
	double x = 0.0, fy, z;

	/*  Misc. efficients for expansion */

	static double a[4] = {0.886226899, -1.645349621,  0.914624893, -0.140543331};
	static double b[4] = {-2.118377725, 1.442710462, -0.329097515, 0.012229801};
	static double c[4] = {-1.970840454, -1.624906493, 3.429567803, 1.641345311};
	static double d[2] = {3.543889200, 1.637067800};

	fy = fabs (y);

	if (fy > 1.0) return (GMT->session.d_NaN);	/* Outside domain */

	if (doubleAlmostEqual (fy, 1.0))
		return (copysign (DBL_MAX, y));	/* Close to +- Inf */

	if (y > 0.7) {		/* Near upper range */
		z = sqrt (-log (0.5 * (1.0 - y)));
		x = (((c[3] * z + c[2]) * z + c[1]) * z + c[0]) / ((d[1] * z + d[0]) * z + 1.0);
	}
	else if (y < -0.7) {	/* Near lower range */
		z = sqrt (-log (0.5 * (1.0 + y)));
		x = -(((c[3] * z + c[2]) * z + c[1]) * z + c[0]) / ((d[1] * z + d[0]) * z + 1.0);
	}
	else {			/* Central range */
		z = y * y;
		x = y * (((a[3] * z + a[2]) * z + a[1]) * z + a[0]) / ((((b[3] * z + b[2]) * z + b[1]) * z + b[0]) * z + 1.0);
	}

	/* Apply two steps of Newton-Raphson correction to improve accuracy */

	x -= (erf (x) - y) / (M_2_SQRTPI * exp (-x * x));
	x -= (erf (x) - y) / (M_2_SQRTPI * exp (-x * x));

	return (x);
}

double gmt_f_pdf (struct GMT_CTRL *GMT, double F, uint64_t nu1, uint64_t nu2) {
	/* Probability density distribution for F */
	double y;

	y = (F < GMT_CONV8_LIMIT) ? 0.0 : sqrt (pow (nu1 * F, (double)nu1) * pow ((double)nu2, (double)nu2) / pow (nu1 * F + nu2, (double)(nu1+nu2))) / (F * gmtstat_beta (GMT, 0.5*nu1, 0.5*nu2));
	return (y);
}

double gmt_f_cdf (struct GMT_CTRL *GMT, double F, uint64_t nu1, uint64_t nu2) {
	/* Cumulative probability density distribution for F */
	double y = 0.0;

	if (F < GMT_CONV8_LIMIT) return 0.0;
	gmtstat_inc_beta (GMT, 0.5*nu1, 0.5*nu2, F*nu1/(F*nu1+nu2), &y);

	return (y);
}

double gmt_t_pdf (struct GMT_CTRL *GMT, double t, uint64_t nu) {
	/* Probability density distribution for Student t */
	double y, n = nu + 1.0, g1 = 0.0, g2 = 0.0;

	gmtstat_ln_gamma_r (GMT, 0.5*n, &g1);
	gmtstat_ln_gamma_r (GMT, 0.5*nu, &g2);
	y = exp (g1 - g2) * pow (1.0 + t*t/nu, -0.5*n) / sqrt (M_PI * nu);
	return (y);
}

double gmt_t_cdf (struct GMT_CTRL *GMT, double t, uint64_t nu) {
	double p;
	/* Cumulative Student t distribution */
	gmt_M_unused(GMT);
	gmtstat_student_t_a (GMT, fabs (t), nu, &p);
	p = 0.5 * p + 0.5;
	if (t < 0.0)
		p = 1.0 - p;
	return (p);
}

double gmt_weibull_pdf (struct GMT_CTRL *GMT, double x, double scale, double shape) {
	double p, z;
	gmt_M_unused(GMT);
	/* Weibull distribution */
	if (x < 0.0) return 0.0;
	z = x / scale;
	p = (shape/scale) * pow (z, shape-1.0) * exp (-pow(z,shape));
	return (p);
}

double gmt_weibull_cdf (struct GMT_CTRL *GMT, double x, double scale, double shape) {
	double p, z;
	gmt_M_unused(GMT);
	/* Cumulative Weibull distribution */
	if (x < 0.0) return 0.0;
	z = x / scale;
	p = 1.0 - exp (-pow (z, shape));
	return (p);
}

double gmt_weibull_crit (struct GMT_CTRL *GMT, double p, double scale, double shape) {
	double z;
	gmt_M_unused(GMT);
	/* Critical values for Weibull distribution */
	z = scale * pow (-log (1.0 - p), 1.0/shape);
	return (z);
}

double gmt_binom_pdf (struct GMT_CTRL *GMT, uint64_t x, uint64_t n, double p) {
	double c;
	/* Binomial distribution */
	c = gmt_combination (GMT, (int)n, (int)x) * pow (p, (int)x) * pow (1.0-p, (int)(n-x));
	return (c);
}

double gmt_binom_cdf (struct GMT_CTRL *GMT, uint64_t x, uint64_t n, double p) {
	/* Cumulative Binomial distribution */
	double c = 0.0;
	if (n > 12)	/* Use Numerical Recipes fast way for larger n */
		gmtstat_inc_beta (GMT, (double)x, (double)(n-x+1), p, &c);
	else {	/* Do the sum instead */
		uint64_t j;
		for (j = 0; j <= x; j++)
			c += gmt_binom_pdf (GMT, j, n, p);
	}
	return (c);
}

double gmt_vonmises_pdf (struct GMT_CTRL *GMT, double x, double mu, double kappa) {
	/* Von Mises 1-D probability density function */
	double p;
	gmt_M_unused(GMT);
	/* Von Mises distribution, expects x and mu in degrees */
	p = exp (kappa * cosd (x - mu)) / (TWO_PI * gmt_i0 (GMT, kappa));
	return (p);
}

double gmt_fisher_pdf (struct GMT_CTRL *GMT, double plon, double plat, double lon, double lat, double kappa) {
	/* Fisher 3-D probability density function centered on (plon, plat) evaluated at
	 * another point (lon, lat), given kappa */
	double p, cos_psi;
	cos_psi = gmtlib_great_circle_dist_cos (GMT, plon, plat, lon, lat);
	p = kappa * exp (kappa * cos_psi) / (2.0 * TWO_PI * sinh (kappa));
	return (p);
}

double gmt_zdist (struct GMT_CTRL *GMT, double x) {
	/* Cumulative Normal (z) distribution */
	gmt_M_unused(GMT);
	return (0.5 * (erf (x / M_SQRT2) + 1.0));
}

double gmt_zcrit (struct GMT_CTRL *GMT, double alpha) {
	double sign;
	/* Critical values for Normal (z) distribution */

	/* Simple since z_a = M_SQRT2 * erf^-1 (1-a) */

	if (alpha > 0.5) {	/* right tail */
		alpha = (1.0 - alpha) * 2.0;
		sign = 1.0;
	}
	else {			/* left tail */
		alpha *= 2.0;
		sign = -1.0;
	}

	return (sign * M_SQRT2 * gmt_erfinv (GMT, 1.0 - alpha));
}

double gmt_tcrit (struct GMT_CTRL *GMT, double alpha, double nu) {
	/* Critical values for Student t-distribution */

	int NU;
	bool done;
	double t_low, t_high, t_mid = 0.0, p_high, p_mid, p, sign;

	if (alpha > 0.5) {	/* right tail */
		p = 1 - (1 - alpha) * 2.0;
		sign = 1.0;
	}
	else {
		p = 1 - alpha * 2.0;
		sign = -1.0;
	}
	t_low = gmt_zcrit (GMT, alpha);
	if (gmt_M_is_dinf (t_low) || gmt_M_is_dnan (t_low)) return (t_low);
	t_high = 5.0;
	NU = irint(nu);
	gmtstat_student_t_a (GMT, t_high, NU, &p_high);
	while (p_high < p) {	/* Must pick higher starting point */
		t_high *= 2.0;
		gmtstat_student_t_a (GMT, t_high, NU, &p_high);
	}

	/* Now, (t_low, p_low) and (t_high, p_high) are bracketing the desired (t,p) */

	done = false;
	while (!done) {
		t_mid = 0.5 * (t_low + t_high);
		gmtstat_student_t_a (GMT, t_mid, NU, &p_mid);
		if (doubleAlmostEqualZero (p_mid, p)) {
			done = true;
		}
		else if (p_mid > p) {	/* Too high */
			t_high = t_mid;
		}
		else { /* p_mid < p */
			t_low = t_mid;
		}
	}
	return (sign * t_mid);
}

double gmt_chi2_pdf (struct GMT_CTRL *GMT, double c, uint64_t nu) {
	/* Probability density distribution for chi-squared */
	double g = 0.0, y;

	gmtstat_ln_gamma_r (GMT, 0.5*nu, &g);
	y = pow (c, 0.5*nu - 1.0) * exp (-0.5 * c - g) / pow (2.0, 0.5 * nu);
	return (y);
}

double gmt_chi2crit (struct GMT_CTRL *GMT, double alpha, double nu) {
	/* Critical values for Chi^2-distribution */

	bool done;
	double chi2_low, chi2_high, chi2_mid = 0.0, p_high, p_mid, p;

	p = 1.0 - alpha;
	chi2_low = 0.0;
	chi2_high = 5.0;
	gmt_chi2 (GMT, chi2_high, nu, &p_high);
	while (p_high > p) {	/* Must pick higher starting point */
		chi2_high *= 2.0;
		gmt_chi2 (GMT, chi2_high, nu, &p_high);
	}

	/* Now, (chi2_low, p_low) and (chi2_high, p_high) are bracketing the desired (chi2,p) */

	done = false;
	while (!done) {
		chi2_mid = 0.5 * (chi2_low + chi2_high);
		gmt_chi2 (GMT, chi2_mid, nu, &p_mid);
		if (doubleAlmostEqualZero (p_mid, p)) {
			done = true;
		}
		else if (p_mid < p) {	/* Too high */
			chi2_high = chi2_mid;
		}
		else { /* p_mid > p */
			chi2_low = chi2_mid;
		}
	}
	return (chi2_mid);
}

double gmt_Fcrit (struct GMT_CTRL *GMT, double alpha, double nu1, double nu2) {
	/* Critical values for F-distribution */

	int NU1, NU2;
	bool done;
	double F_low, F_high, F_mid = 0.0, p_high, p_mid, p, chisq1, chisq2;

	F_high = 5.0;
	p = 1.0 - alpha;
	F_low = 0.0;
	gmtstat_F_to_ch1_ch2 (GMT, F_high, nu1, nu2, &chisq1, &chisq2);
	NU1 = irint (nu1);
	NU2 = irint (nu2);
	gmtstat_f_q (GMT, chisq1, NU1, chisq2, NU2, &p_high);
	while (p_high > p) {	/* Must pick higher starting point */
		F_high *= 2.0;
		gmtstat_F_to_ch1_ch2 (GMT, F_high, nu1, nu2, &chisq1, &chisq2);
		gmtstat_f_q (GMT, chisq1, NU1, chisq2, NU2, &p_high);
	}

	/* Now, (F_low, p_low) and (F_high, p_high) are bracketing the desired (F,p) */

	done = false;
	while (!done) {
		F_mid = 0.5 * (F_low + F_high);
		gmtstat_F_to_ch1_ch2 (GMT, F_mid, nu1, nu2, &chisq1, &chisq2);
		gmtstat_f_q (GMT, chisq1, NU1, chisq2, NU2, &p_mid);
		if (doubleAlmostEqualZero (p_mid, p)) {
			done = true;
		}
		else if (p_mid < p) {	/* Too high */
			F_high = F_mid;
		}
		else { /* p_mid > p */
			F_low = F_mid;
		}
	}
	return (F_mid);
}

static inline uint64_t gmtstat_mix64 (uint64_t a, uint64_t b, uint64_t c) {
	/* Mix 3 64-bit values, from lookup8.c by Bob Jenkins
	 * (http://burtleburtle.net/bob/index.html) */
	a -= b; a -= c; a ^= (c>>43);
	b -= c; b -= a; b ^= (a<<9);
	c -= a; c -= b; c ^= (b>>8);
	a -= b; a -= c; a ^= (c>>38);
	b -= c; b -= a; b ^= (a<<23);
	c -= a; c -= b; c ^= (b>>5);
	a -= b; a -= c; a ^= (c>>35);
	b -= c; b -= a; b ^= (a<<49);
	c -= a; c -= b; c ^= (b>>11);
	a -= b; a -= c; a ^= (c>>12);
	b -= c; b -= a; b ^= (a<<18);
	c -= a; c -= b; c ^= (b>>22);
	return c;
}

double gmt_rand (struct GMT_CTRL *GMT) {
	/* Uniform random number generator.  Will return values
	 * x so that 0.0 < x < 1.0 occurs with equal probability. */
	static unsigned seed = 0;
	double random_val;

	while (seed == 0) { /* repeat in case of unsigned overflow */
		/* Initialize random seed, idea from Jonathan
		 * Wright (http://stackoverflow.com/q/322938) */
		seed = (unsigned) gmtstat_mix64 (clock(), time(NULL), getpid());
		srand (seed);
	}

	/* generate random number */
	random_val = rand () / (double) RAND_MAX;

	if (random_val == 0.0 || random_val >= 1.0)
		/* Ensure range (0.0,1.0) */
		return gmt_rand (GMT);

	return random_val;
}

double gmt_nrand (struct GMT_CTRL *GMT) {
	/* Gaussian random number generator based on gasdev of
	 * Press et al, Numerical Recipes, 2nd edition.  Will
	 * return values that have zero mean and unit variance.
	 */

	static int iset = 0;
	static double gset;
	double fac, r, v1, v2;

	if (iset == 0) {	/* We don't have an extra deviate handy, so */
		do {
			v1 = 2.0 * gmt_rand (GMT) - 1.0;	/* Pick two uniform numbers in the -1/1/-1/1 square */
			v2 = 2.0 * gmt_rand (GMT) - 1.0;
			r = v1 * v1 + v2 * v2;
		} while (r >= 1.0 || r == 0.0);	/* Keep trying until v1,v2 is inside unit circle */

		fac = sqrt (-2.0 * log (r) / r);

		/* Now make Box-Muller transformation to get two normal deviates.  Return
		 * one and save the other for the next time gmt_nrand is called */

		gset = v1 * fac;
		iset = 1;	/* Set flag for next time */
		return (v2 * fac);
	}
	else {
		iset = 0;	/* Take old value, reset flag */
		return (gset);
	}
}

double gmt_lrand (struct GMT_CTRL *GMT) {
	/* Laplace random number generator.  As nrand, it will
	 * return values that have zero mean and unit variance.
	 */

	double rand_0_to_1;

	rand_0_to_1 = gmt_rand (GMT);	/* Gives uniformly distributed random values in 0-1 range */
	return (((rand_0_to_1 <= 0.5) ? log (2.0 * rand_0_to_1) : -log (2.0 * (1.0 - rand_0_to_1))) / M_SQRT2);
}

void gmt_chi2 (struct GMT_CTRL *GMT, double chi2, double nu, double *prob) {
	/* Evaluate probability that chi2 will exceed the
	 * theoretical chi2 by chance. */

	*prob = gmtstat_gammq (GMT, 0.5 * nu, 0.5 * chi2);
}

double gmt_poissonpdf (struct GMT_CTRL *GMT, double k, double lambda) {
	/* Evaluate PDF for Poisson Distribution */
	return pow (lambda, k) * exp (-lambda) / gmt_factorial (GMT, irint (k));
}

void gmt_poisson_cdf (struct GMT_CTRL *GMT, double k, double mu, double *prob) {
	/* evaluate Cumulative Poisson Distribution */

	*prob = (k == 0.0) ? exp (-mu) : gmtstat_gammq (GMT, k+1.0, mu);
}

double gmt_mean_and_std (struct GMT_CTRL *GMT, double *x, uint64_t n, double *std) {
	/* Return the standard deviation of the non-NaN values in x */
	uint64_t k, m = 0;
	double dx, mean = 0.0, sum2 = 0.0;
	for (k = 0; k < n; k++) {	/* Use Welford (1962) algorithm to compute mean and corrected sum of squares */
		if (gmt_M_is_dnan (x[k])) continue;
		m++;
		dx = x[k] - mean;
		mean += dx / m;
		sum2 += dx * (x[k] - mean);
	}
	*std = (m > 1) ? sqrt (sum2 / (m-1.0)) : GMT->session.d_NaN;
	return (mean);
}

double gmt_std_weighted (struct GMT_CTRL *GMT, double *x, double *w, double wmean, uint64_t n) {
	/* Return the weighted standard deviation of the non-NaN values in x.
	 * If w == NULL then a regular std is computed. */
	uint64_t k, m = 0;
	double dx, sumw = 0.0, sum2 = 0.0, wk = 1.0;
	for (k = 0; k < n; k++) {
		if (gmt_M_is_dnan (x[k])) continue;
		if (w) {
			if (gmt_M_is_dnan (w[k])) continue;
			if (gmt_M_is_zero (w[k])) continue;
			wk = w[k];
		}
		dx = x[k] - wmean;
		sum2 += wk * dx * dx;
		sumw += wk;
		m++;	/* Number of points with nonzero weights */
	}
	return (m > 1) ? sqrt (sum2 / (((m-1.0) * sumw) / m)) : GMT->session.d_NaN;
}

int gmt_median (struct GMT_CTRL *GMT, double *x, uint64_t n, double xmin, double xmax, double m_initial, double *med) {
	double lower_bound, upper_bound, m_guess, t_0, t_1, t_middle;
	double lub, glb, xx, temp;
	uint64_t i;
	int64_t n_above, n_below, n_equal, n_lub, n_glb, one;	/* These must be signed integers (PW: Why? -> (unsigned)x - (unsigned)y will never become negative) */
	int iteration = 0;
	bool finished = false;

	if (n == 0) {	/* No data, so no defined median */
		*med = GMT->session.d_NaN;
		return (1);
	}
	if (n == 1) {
		*med = x[0];
		return (1);
	}
	if (n == 2) {
		*med = 0.5 * (x[0] + x[1]);
		return (1);
	}

	m_guess = m_initial;
	lower_bound = xmin;
	upper_bound = xmax;
	one = 1;
	t_0 = 0.0;
	t_1 = (double)(n - one);
	t_middle = 0.5 * t_1;

	do {

		n_above = n_below = n_equal = n_lub = n_glb = 0;
		lub = xmax;
		glb = xmin;

		for (i = 0; i < n; i++) {

			xx = x[i];
			if (xx == m_guess)
				n_equal++;
			else if (xx > m_guess) {
				n_above++;
				if (xx < lub) {
					lub = xx;
					n_lub = one;
				}
				else if (xx == lub)
					n_lub++;
			}
			else {
				n_below++;
				if (xx > glb) {
					glb = xx;
					n_glb = one;
				}
				else if (xx == glb)
					n_glb++;
			}
		}

		iteration++;

		/* Now test counts, watch multiple roots, think even/odd:  */

		if ((int64_abs (n_above - n_below)) <= n_equal) {
			*med = (n_equal) ? m_guess : 0.5 * (lub + glb);
			finished = true;
		}
		else if ((int64_abs ((n_above - n_lub) - (n_below + n_equal))) < n_lub) {
			*med = lub;
			finished = true;
		}
		else if ((int64_abs ((n_below - n_glb) - (n_above + n_equal))) < n_glb) {
			*med = glb;
			finished = true;
		}
		/* Those cases found the median; the next two will forecast a new guess:  */

		else if (n_above > (n_below + n_equal)) {  /* Guess is too low  */
			lower_bound = m_guess;
			t_0 = (double)(n_below + n_equal - one);
			temp = lower_bound + (upper_bound - lower_bound) * (t_middle - t_0) / (t_1 - t_0);
			m_guess = (temp > lub) ? temp : lub;	/* Move guess at least to lub  */
		}
		else if (n_below > (n_above + n_equal)) {  /* Guess is too high  */
			upper_bound = m_guess;
			t_1 = (double)(n_below + n_equal - one);
			temp = lower_bound + (upper_bound - lower_bound) * (t_middle - t_0) / (t_1 - t_0);
			m_guess = (temp < glb) ? temp : glb;	/* Move guess at least to glb  */
		}
		else {	/* If we get here, I made a mistake!  */
			GMT_Report (GMT->parent, GMT_MSG_ERROR, "Internal goof in gmt_median; please report to developers!\n");
			*med = GMT->session.d_NaN;
			return GMT_NOTSET;
		}

	} while (!finished);

	/* That's all, folks!  */
	return (iteration);
}

double gmt_mean_weighted (struct GMT_CTRL *GMT, double *x, double *w, uint64_t n) {
	/* Return the weighted mean of x given weights w */
	uint64_t k;
	double sum_xw = 0.0, sum_w = 0.0;

	if (n == 0) return (GMT->session.d_NaN);	/* No data, so no defined mean */
	for (k = 0; k < n; k++) {
		sum_w  += w[k];
		sum_xw += x[k] * w[k];
	}
	if (sum_w == 0.0) return (GMT->session.d_NaN);	/* No weights, so no defined mean */
	return (sum_xw / sum_w);
}

double gmt_quantile_weighted (struct GMT_CTRL *GMT, struct GMT_OBSERVATION *data, uint64_t n, double quantile) {
	uint64_t k;
	double weight_half = 0.0, weight_count;

	if (n == 0) return (GMT->session.d_NaN);	/* No data, so no defined mode */
	else if (n == 1) return (data[0].value);	/* Single point, so also the mode */

	/* First sort data on z */

	qsort (data, n, sizeof (struct GMT_OBSERVATION), gmtlib_compare_observation);

	/* Find weight sum, then get half-value */

	for (k = 0; k < n; k++) weight_half += data[k].weight;
	weight_half *= quantile;	/* Normally quantile = 0.5 hence the name "half" */

	/* Determine the point where we hit the desired quantile */

	k = 0;	weight_count = data[k].weight;
	while (weight_count < weight_half) weight_count += data[++k].weight;	/* Wind up until weight_count hits the mark */

	return ((double)((weight_count == weight_half) ? 0.5 * (data[k].value + data[k+1].value) : data[k].value));
}

double gmt_median_weighted (struct GMT_CTRL *GMT, struct GMT_OBSERVATION *data, uint64_t n) {
	/* Just hardwire quantile to 0.5 */
	return gmt_quantile_weighted (GMT, data, n, 0.5);
}

double gmt_mode_weighted (struct GMT_CTRL *GMT, struct GMT_OBSERVATION *data, uint64_t n) {
	/* Looks for the "shortest 50%". This means that when the cumulative weight
	   (y) is plotted against the value (x) then the line between (xi,yi) and
	   (xj,yj) should be the steepest for any combination where (yj-yi) is 50%
	   of the total sum of weights */

	double top, bottom, wsum, p, p_max, mode;
	uint64_t i, j;

	if (n == 0) return (GMT->session.d_NaN);	/* No data, so no defined mode */
	else if (n == 1) return (data[0].value);	/* Single point is its own mode */

	/* First sort data on z */
	qsort (data, n, sizeof (struct GMT_OBSERVATION), gmtlib_compare_observation);

	/* Compute the total weight */
	for (wsum = 0.0, i = 0; i < n; i++) wsum += data[i].weight;

	/* Do some initializations */
	wsum = 0.5 * wsum;	/* Sets the 50% range */

	/* First check if any single point has 50% or more of the total weights; if so we are done */
	for (i = 0; i < n; i++) if (data[i].weight >= wsum) return data[i].value;

	/* Some more initializations */
	top = p_max = 0.0;
	mode = 0.5 * (data[0].value + data[n-1].value);

	for (i = j = 0; j < n; j++) {
		top += data[j].weight;
		if (top < wsum) continue;
		while (top > wsum && i < j) top -= data[i++].weight;
		bottom = data[j].value - data[i].value;

		/* If all is comprised in one point or if a lot of values are the same,
		   then we have a spike. Maybe another logic is needed to handle
		   multiple spikes in the data */
		if (bottom == 0.0) return (data[i].value);

		p = top / bottom;
		if (p > p_max) {
			p_max = p;
			mode = 0.5 * (data[i].value + data[j].value);
		}
	}
	return (mode);
}

int gmt_mode (struct GMT_CTRL *GMT, double *x, uint64_t n, uint64_t j, bool sort, int mode_selection, unsigned int *n_multiples, double *mode_est) {
	uint64_t i, istop;
	unsigned int multiplicity;
	double mid_point_sum = 0.0, length, short_length = DBL_MAX, this_mode;

	if (n == 0) {	/* No data, so no defined mode */
		*mode_est = GMT->session.d_NaN;
		return (0);
	}
	if (n == 1) {
		*mode_est = x[0];
		return (0);
	}

	if (sort) gmt_sort_array (GMT, x, n, GMT_DOUBLE);
	while (n && gmt_M_is_dnan (x[n-1])) n--;	/* Skip any NaNs at end of sorted array */
	istop = n - j;
	multiplicity = 0;

	for (i = 0; i < istop; i++) {
		length = x[i + j] - x[i];
		if (length < 0.0) {
			GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmt_mode: Array not sorted in non-decreasing order.\n");
			return (GMT_NOTSET);
		}
		else if (length == short_length) {	/* Possibly multiple mode */
			switch (mode_selection) {
				case -1:	/* Always pick lowest mode */
					this_mode = 0.5 * (x[i + j] + x[i]);
					if (this_mode < mid_point_sum) mid_point_sum = this_mode;
					break;
				case 0:		/* Return average of all modes */
					multiplicity++;
					mid_point_sum += (0.5 * (x[i + j] + x[i]));
					break;
				case +1:	/* Always pick highest mode */
					this_mode = 0.5 * (x[i + j] + x[i]);
					if (this_mode > mid_point_sum) mid_point_sum = this_mode;
					break;
			}
		}
		else if (length < short_length) {	/* Update current best mode estimate */
			multiplicity = 1;
			mid_point_sum = (0.5 * (x[i + j] + x[i]));
			short_length = length;
		}
	}

	if (multiplicity > 1) {	/* Found more than 1 mode; return mean of them all */
		mid_point_sum /= multiplicity;
		(*n_multiples) += multiplicity;
	}

	*mode_est = mid_point_sum;
	return (0);
}

int gmt_mode_f (struct GMT_CTRL *GMT, gmt_grdfloat *x, uint64_t n, uint64_t j, bool sort, int mode_selection, unsigned int *n_multiples, double *mode_est) {
	uint64_t i, istop;
	unsigned int multiplicity;
	double mid_point_sum = 0.0, length, short_length = FLT_MAX, this_mode;

	if (n == 0) {	/* No data, so no defined mode */
		*mode_est = GMT->session.d_NaN;
		return (0);
	}
	if (n == 1) {
		*mode_est = x[0];
		return (0);
	}
	if (sort) gmt_sort_array (GMT, x, n, GMT_FLOAT);

	istop = n - j;
	multiplicity = 0;

	for (i = 0; i < istop; i++) {
		length = x[i + j] - x[i];
		if (length < 0.0) {
			GMT_Report (GMT->parent, GMT_MSG_WARNING, "gmt_mode_f: Array not sorted in non-decreasing order.\n");
			return (GMT_NOTSET);
		}
		else if (length == short_length) {	/* Possibly multiple mode */
			switch (mode_selection) {
				case -1:	/* Always pick lowest mode */
					this_mode = 0.5 * (x[i + j] + x[i]);
					if (this_mode < mid_point_sum) mid_point_sum = this_mode;
					break;
				case 0:		/* Return average of all modes */
					multiplicity++;
					mid_point_sum += (0.5 * (x[i + j] + x[i]));
					break;
				case +1:	/* Always pick highest mode */
					this_mode = 0.5 * (x[i + j] + x[i]);
					if (this_mode > mid_point_sum) mid_point_sum = this_mode;
					break;
			}
		}
		else if (length < short_length) {
			multiplicity = 1;
			mid_point_sum = (0.5 * (x[i + j] + x[i]));
			short_length = length;
		}
	}

	if (multiplicity > 1) {	/* Found more than 1 mode; return mean of them all */
		mid_point_sum /= multiplicity;
		(*n_multiples) += multiplicity;
	}

	*mode_est = mid_point_sum;
	return (0);
}

/* Replacement slower functions until we figure out the problem with the algorithm */

void gmt_getmad (struct GMT_CTRL *GMT, double *x, uint64_t n, double location, double *scale) {
	uint64_t i;
	double med, *dev = NULL;

	if (n == 0) {	/* No data, so cannot define MAD */
		*scale = GMT->session.d_NaN;
		return;
	}
	else if (n == 1) {	/* Single point has no deviation */
		*scale = 0.0;
		return;
	}

	if ((dev = gmt_M_memory (GMT, NULL, n, double)) == NULL) return;
	for (i = 0; i < n; i++) dev[i] = fabs (x[i] - location);
	gmt_sort_array (GMT, dev, n, GMT_DOUBLE);
	/* Eliminate any NaNs which would have congregated at the end of the array */
	for (i = n; i > 0 && gmt_M_is_dnan (dev[i-1]); i--);
	if (i)
		med = (i%2) ? dev[i/2] : 0.5 * (dev[(i-1)/2] + dev[i/2]);
	else
		med = GMT->session.d_NaN;
	gmt_M_free (GMT, dev);
	*scale = MAD_NORMALIZE * med;
}

void gmt_getmad_f (struct GMT_CTRL *GMT, gmt_grdfloat *x, uint64_t n, double location, double *scale) {
	uint64_t i;
	gmt_grdfloat *dev = NULL;
	double med;

	if (n == 0) {	/* No data, so cannot define MAD */
		*scale = GMT->session.d_NaN;
		return;
	}
	else if (n == 1) {	/* Single point has no deviation */
		*scale = 0.0;
		return;
	}
	if ((dev = gmt_M_memory (GMT, NULL, n, double)) == NULL) return;
	for (i = 0; i < n; i++) dev[i] = (gmt_grdfloat) fabs (x[i] - location);
	gmt_sort_array (GMT, dev, n, GMT_FLOAT);
	for (i = n; i > 0 && gmt_M_is_fnan (dev[i-1]); i--);
	if (i)
		med = (i%2) ? dev[i/2] : 0.5 * (dev[(i-1)/2] + dev[i/2]);
	else
		med = GMT->session.d_NaN;
	gmt_M_free (GMT, dev);
	*scale = MAD_NORMALIZE * med;
}

double gmt_extreme (struct GMT_CTRL *GMT, double x[], uint64_t n, double x_default, int kind, int way) {
	/* Returns the extreme value in the x array according to:
	*  kind: -1 means only consider negative values, including zero.
	*  kind:  0 means consider all values.
	*  kind: +1 means only consider positive values, including zero.
	*  way:  -1 means look for minimum.
	*  way:  +1 means look for maximum.
	* If kind is non-zero we assign x_default is no values are found.
	* If kind == 0 we expect x_default to be set so that x[0] will reset x_select.
	*/

	uint64_t i, k;
	double x_select = GMT->session.d_NaN;

	if (n == 0) return (x_select);	/* No data, so no defined extreme value */
	for (i = k = 0; i < n; i++) {
		if (kind == -1 && x[i] > 0.0) continue;
		if (kind == +1 && x[i] < 0.0) continue;
		if (k == 0) x_select = x[i];
		if (way == -1 && x[i] < x_select) x_select = x[i];
		if (way == +1 && x[i] > x_select) x_select = x[i];
		k++;
	}

	return ((k) ? x_select : x_default);
}

int gmt_chebyshev (struct GMT_CTRL *GMT, double x, int n, double *t) {
	/* Calculates the n'th Chebyshev polynomial at x */

	double x2, a, b;

	if (n < 0) gmt_M_err_pass (GMT, GMT_CHEBYSHEV_NEG_ORDER, "");
	if (fabs (x) > 1.0) gmt_M_err_pass (GMT, GMT_CHEBYSHEV_BAD_DOMAIN, "");

	switch (n) {	/* Testing the order of the polynomial */
		case 0:
			*t = 1.0;
			break;
		case 1:
			*t = x;
			break;
		case 2:
			*t = 2.0 * x * x - 1.0;
			break;
		case 3:
			*t = x * (4.0 * x * x - 3.0);
			break;
		case 4:
			x2 = x * x;
			*t = 8.0 * x2 * (x2 - 1.0) + 1.0;
			break;
		default:	/* For higher degrees we do the recursion */
			gmt_chebyshev (GMT, x, n-1, &a);
			gmt_chebyshev (GMT, x, n-2, &b);
			*t = 2.0 * x * a - b;
			break;
	}

	return (GMT_NOERROR);
}

double gmt_corrcoeff (struct GMT_CTRL *GMT, double *x, double *y, uint64_t n, unsigned int mode) {
	/* Returns plain correlation coefficient, r.
	 * If mode = 1 we assume mean(x) = mean(y) = 0.
	 */

	uint64_t i, n_use;
	double xmean = 0.0, ymean = 0.0, dx, dy, vx, vy, vxy, r;

	if (n == 0) return (GMT->session.d_NaN);	/* No data, so no defined correlation */
	if (mode == 0) {
		for (i = n_use = 0; i < n; i++) {
			if (gmt_M_is_dnan (x[i]) || gmt_M_is_dnan (y[i])) continue;
			xmean += x[i];
			ymean += y[i];
			n_use++;
		}
		if (n_use == 0) return (GMT->session.d_NaN);
		xmean /= (double)n_use;
		ymean /= (double)n_use;
	}

	vx = vy = vxy = 0.0;
	for (i = n_use = 0; i < n; i++) {
		if (gmt_M_is_dnan (x[i]) || gmt_M_is_dnan (y[i])) continue;
		dx = x[i] - xmean;
		dy = y[i] - ymean;
		vx += dx * dx;
		vy += dy * dy;
		vxy += dx * dy;
	}

	r = vxy / sqrt (vx * vy);
	return (r);
}

double gmt_corrcoeff_f (struct GMT_CTRL *GMT, gmt_grdfloat *x, gmt_grdfloat *y, uint64_t n, unsigned int mode) {
	/* Returns plain correlation coefficient, r.
	 * If mode = 1 we assume mean(x) = mean(y) = 0.
	 */

	uint64_t i, n_use;
	double xmean = 0.0, ymean = 0.0, dx, dy, vx, vy, vxy, r;

	if (n == 0) return (GMT->session.d_NaN);	/* No data, so no defined correlation */
	if (mode == 0) {
		for (i = n_use = 0; i < n; i++) {
			if (gmt_M_is_fnan (x[i]) || gmt_M_is_fnan (y[i])) continue;
			xmean += (double)x[i];
			ymean += (double)y[i];
			n_use++;
		}
		if (n_use == 0) return (GMT->session.d_NaN);
		xmean /= (double)n_use;
		ymean /= (double)n_use;
	}

	vx = vy = vxy = 0.0;
	for (i = n_use = 0; i < n; i++) {
		if (gmt_M_is_fnan (x[i]) || gmt_M_is_fnan (y[i])) continue;
		dx = (double)x[i] - xmean;
		dy = (double)y[i] - ymean;
		vx += dx * dx;
		vy += dy * dy;
		vxy += dx * dy;
	}

	r = vxy / sqrt (vx * vy);
	return (r);
}

double gmt_quantile (struct GMT_CTRL *GMT, double *x, double q, uint64_t n) {
	/* Returns the q'th (q in percent) quantile of x (assumed sorted).
	 * q is expected to be 0 < q < 100 */

	uint64_t i_f;
	double p, f, df;

	if (n == 0) return (GMT->session.d_NaN);	/* No data, so no defined quantile */
	else if (n == 1) return (x[0]);			/* Single point so is also any quantile */
	else if (q == 0.0) return (x[0]);		/* 0% quantile == min(x) */
	while (n > 1 && gmt_M_is_dnan (x[n-1])) n--;	/* Skip any NaNs at the end of x */
	if (q == 100.0) return (x[n-1]);		/* 100% quantile == max(x) */
	f = (n - 1) * q / 100.0;
	i_f = (uint64_t)floor (f);
	if ((df = (f - (double)i_f)) > 0.0)		/* Must interpolate between the two neighbors */
		p = x[i_f+1] * df + x[i_f] * (1.0 - df);
	else						/* Exactly on a node */
		p = x[i_f];

	return (p);
}

double gmt_quantile_f (struct GMT_CTRL *GMT, gmt_grdfloat *x, double q, uint64_t n) {
	/* Returns the q'th (q in percent) quantile of x (assumed sorted).
	 * q is expected to be 0 < q < 100 */

	uint64_t i_f;
	double p, f, df;

	if (n == 0) return (GMT->session.d_NaN);	/* No data, so no defined quantile */
	else if (n == 1) return (x[0]);			/* Single point so is also any quantile */
	else if (q == 0.0) return ((double)x[0]);	/* 0% quantile == min(x) */
	while (n > 1 && gmt_M_is_fnan (x[n-1])) n--;	/* Skip any NaNs at the end of x */
	if (q == 100.0) return ((double)x[n-1]);	/* 100% quantile == max(x) */
	f = (n - 1) * q / 100.0;
	i_f = (uint64_t)floor (f);
	if ((df = (f - (double)i_f)) > 0.0)		/* Must interpolate between the two neighbors */
		p = (double)(x[i_f+1] * df + x[i_f] * (1.0 - df));
	else						/* Exactly on a node */
		p = (double)x[i_f];

	return (p);
}

double gmt_psi (struct GMT_CTRL *P, double zz[], double p[]) {
/* Psi     Psi (or Digamma) function for complex arguments z.
*
*                 d
*        Psi(z) = --log(Gamma(z))
*                 dz
*
* zz[GMT_RE] is real and zz[GMT_IM] is imaginary component; same for p on output (only if p != NULL).
* We also return the real component as function result.
*/
	static double c[15] = { 0.99999999999999709182, 57.156235665862923517, -59.597960355475491248,
			14.136097974741747174, -0.49191381609762019978, 0.33994649984811888699e-4,
			0.46523628927048575665e-4, -0.98374475304879564677e-4, 0.15808870322491248884e-3,
			-0.21026444172410488319e-3, 0.21743961811521264320e-3, -0.16431810653676389022e-3,
			0.84418223983852743293e-4, -0.26190838401581408670e-4, 0.36899182659531622704e-5};
	double z[2], g[2], dx[2], dd[2], d[2], n[2], gg[2], f[2], x0, A[2], B[2], C[2], sx, cx, e;
	int k;

	if (zz[GMT_IM] == 0.0 && rint(zz[GMT_RE]) == zz[GMT_RE] && zz[GMT_RE] <= 0.0) {
		if (p) { p[GMT_RE] = P->session.d_NaN; p[GMT_IM] = 0.0;}
		return (P->session.d_NaN);	/* Singular points */
	}

	z[GMT_RE] = zz[GMT_RE];	z[GMT_IM] = zz[GMT_IM];
	if ((x0 = z[GMT_RE]) < 0.5) {	/* reflection point */
		z[GMT_RE] = 1.0 - z[GMT_RE];
		z[GMT_IM] = -z[GMT_IM];
	}

	/* Lanczos approximation */

	g[GMT_RE] = 607.0/128.0;	g[GMT_IM] = 0.0; /* best results when 4<=g<=5 */
	n[GMT_RE] = d[GMT_RE] = n[GMT_IM] = d[GMT_IM] = 0.0;
	for (k = 14; k > 0; k--) {
		A[GMT_RE] = 1.0;	A[GMT_IM] = 0.0;
		B[GMT_RE] = z[GMT_RE] + k - 1.0;	B[GMT_IM] = z[GMT_IM];
		gmtstat_Cdiv (A, B, dx);
		dd[GMT_RE] = c[k] * dx[GMT_RE];	dd[GMT_IM] = c[k] * dx[GMT_IM];
		d[GMT_RE] += dd[GMT_RE];	d[GMT_IM] += dd[GMT_IM];
		gmtstat_Cmul (dd, dx, B);
		n[GMT_RE] -= B[GMT_RE];	n[GMT_IM] -= B[GMT_IM];
	}
	d[GMT_RE] += c[GMT_RE];
	gg[GMT_RE] = z[GMT_RE] + g[GMT_RE] - 0.5;	gg[GMT_IM] = z[GMT_IM];
	gmtstat_Cdiv (n, d, A);
	gmtstat_Cdiv (g, gg, B);
	f[GMT_RE] = log (hypot(gg[GMT_RE], gg[GMT_IM])) + A[GMT_RE] - B[GMT_RE];
	f[GMT_IM] = atan2 (gg[GMT_IM], gg[GMT_RE])  + A[GMT_IM] - B[GMT_IM];
	if (x0 < 0.5) {
		C[GMT_RE] = M_PI * zz[GMT_RE];	C[GMT_IM] = M_PI * zz[GMT_IM];
		e = exp (-2*C[GMT_IM]);	sx = sin (2*C[GMT_RE]);	cx = cos (2*C[GMT_RE]);
		A[GMT_RE] = -e * sx;	A[GMT_IM] = e * cx + 1.0;
		B[GMT_RE] = e * cx - 1.0;	B[GMT_IM] = e * sx;
		gmtstat_Cdiv (A, B, C);
		f[GMT_RE] -= M_PI * C[GMT_RE];	f[GMT_IM] -= M_PI * C[GMT_IM];
	}
	if (p) {
		p[GMT_RE] = f[GMT_RE];
		p[GMT_IM] = f[GMT_IM];
	}
	return (f[GMT_RE]);
}

#ifndef M_SQRT_PI
#define M_SQRT_PI 1.772453850905516
#endif

#define PV_RE 0
#define PV_IM 1
#define QV_RE 2
#define QV_IM 3

void gmt_PvQv (struct GMT_CTRL *GMT, double x, double v_ri[], double pq[], unsigned int *iter) {
	/* Here, -1 <= x <= +1, v_ri is an imaginary number [r,i], and we return
	 * the real amd imaginary parts of Pv(x) and Qv(x) in the pq array.
	 * Based on recipe in An Atlas of Functions */

	bool p_set, q_set;
	double M, L, K, Xn, x2, k, k1, ep, em, sx, cx, fact;
	double a[2], v[2], vp1[2], G[2], g[2], u[2], t[2], f[2];
	double R[2], r[2], z[2], s[2], c[2], w[2], tmp[2], X[2], A[2], B[2];

	*iter = 0;
	pq[PV_RE] = pq[QV_RE] = pq[PV_IM] = pq[QV_IM] = 0.0;	/* Initialize all answers to zero first */
	p_set = q_set = false;
	if (x == -1 && v_ri[GMT_IM] == 0.0) {	/* Check special values for real nu when x = -1 */
			/* Special Pv(-1) values */
		if ((v_ri[GMT_RE] > 0.0 && fmod (v_ri[GMT_RE], 2.0) == 1.0) || (v_ri[GMT_RE] < 0.0 && fmod (v_ri[GMT_RE], 2.0) == 0.0)) {	/* v = 1,3,5,.. or -2, -4, -6 */
			pq[PV_RE] = -1.0; p_set = true;
		}
		else if ((v_ri[GMT_RE] >= 0.0 && fmod (v_ri[GMT_RE], 2.0) == 0.0) || (v_ri[GMT_RE] < 0.0 && fmod (v_ri[GMT_RE]+1.0, 2.0) == 0.0)) {	/* v = 0,2,4,6 or -1,-3,-5,-7 */
			pq[PV_RE] = 1.0; p_set = true;
		}
		else if (v_ri[GMT_RE] > 0.0 && ((fact = v_ri[GMT_RE]-2.0*floor(v_ri[GMT_RE]/2.0)) < 1.0 && fact > 0.0)) { /* 0 < v < 1, 2 < v < 3, 4 < v < 5, ... */
			pq[PV_RE] = GMT->session.d_NaN; p_set = true;	/* -inf */
		}
		else if (v_ri[GMT_RE] < 1.0 && ((fact = v_ri[GMT_RE]-2.0*floor(v_ri[GMT_RE]/2.0)) < 1.0 && fact > 0.0)) {	/* -2 < v < -1, -4 < v < -3, -6 < v < -5 */
			pq[PV_RE] = GMT->session.d_NaN; p_set = true;	/* -inf */
		}
		else if (v_ri[GMT_RE] > 1.0 && (v_ri[GMT_RE]-2.0*floor(v_ri[GMT_RE]/2.0)) > 1.0) {	/* 1 < v < 2, 3 < v < 4, 5 < v < 6, .. */
			pq[PV_RE] = GMT->session.d_NaN; p_set = true;	/* +inf */
		}
		else if (v_ri[GMT_RE] < 2.0 && ( v_ri[GMT_RE]-2.0*floor(v_ri[GMT_RE]/2.0)) > 1.0) {	/* -3 < v < -2, -5 < v < -4, -7 < v < -6, .. */
			pq[PV_RE] = GMT->session.d_NaN; p_set = true;	/* +inf */
		}
		/* Special Qv(-1) values */
		if (v_ri[GMT_RE] > 0.0 && fmod (2.0 * v_ri[GMT_RE] - 1.0, 4.0) == 0.0) {	/* v = 1/2, 5/2, 9/2, ... */
			pq[QV_RE] = -M_PI_2; q_set = true;
		}
		else if (v_ri[GMT_RE] > -1.0 && fmod (2.0 * v_ri[GMT_RE] + 1.0, 4.0) == 0.0) {	/* v = -1/2, 3/2, 7/2, ... */
			pq[QV_RE] = M_PI_2; q_set = true;
		}
		else if (v_ri[GMT_RE] < -1.0 && fmod (2.0 * v_ri[GMT_RE] - 1.0, 4.0) == 0.0) {	/* v = -3/2, -7/2, -11/2, ... */
			pq[QV_RE] = -M_PI_2; q_set = true;
		}
		else if (v_ri[GMT_RE] < -2.0 && fmod (2.0 * v_ri[GMT_RE] + 1.0, 4.0) == 0.0) {	/* v = -5/2, -9/2, -13/2, ... */
			pq[QV_RE] = M_PI_2; q_set = true;
		}
		else {	/* Either -inf or +inf */
			pq[QV_RE] = GMT->session.d_NaN; q_set = true;
		}
	}
	else if (x == +1 && v_ri[GMT_IM] == 0.0) {	/* Check special values for real nu when x = +1 */
		pq[PV_RE] = 1.0; p_set = true;
		pq[QV_RE] = GMT->session.d_NaN; q_set = true;
	}
	if (p_set && q_set) return;

	/* General case of |x| < 1 */

	a[0] = a[1] = R[GMT_RE] = 1.0;	R[GMT_IM] = 0.0;
	v[GMT_RE] = v_ri[GMT_RE];	v[GMT_IM] = v_ri[GMT_IM];
	gmtstat_Cmul (v, v, z);
	z[GMT_RE] = v[GMT_RE] - z[GMT_RE];	z[GMT_IM] = v[GMT_IM] - z[GMT_IM];
	K = 4.0 * sqrt (gmtstat_Cabs(z));
	vp1[GMT_RE] = v[GMT_RE] + 1.0;	vp1[GMT_IM] = v[GMT_IM];
	if ((gmtstat_Cabs(vp1) + floor(vp1[GMT_RE])) == 0.0) {
		a[0] = GMT->session.d_NaN;
		a[1] = 0.0;
		v[GMT_RE] = -1 - v[GMT_RE];
		v[GMT_IM] = -v[GMT_IM];
	}
	z[GMT_RE] = 0.5 * M_PI * v[GMT_RE];	z[GMT_IM] = 0.5 * M_PI * v[GMT_IM];
	ep = exp (z[GMT_IM]);	em = exp (-z[GMT_IM]);
	sincos (z[GMT_RE], &sx, &cx);
	s[GMT_RE] = 0.5 * sx * (em + ep);
	s[GMT_IM] = -0.5 * cx * (em - ep);
	c[GMT_RE] = 0.5 * cx * (em + ep);
	c[GMT_IM] = 0.5 * sx * (em - ep);
	tmp[GMT_RE] = 0.5 + v[GMT_RE];	tmp[GMT_IM] = v[GMT_IM];
	gmtstat_Cmul (tmp, tmp, w);
	z[GMT_IM] = v[GMT_IM];
	while (v[GMT_RE] <= 6.0) {
		v[GMT_RE] = v[GMT_RE] + 2.0;
		z[GMT_RE] = v[GMT_RE] - 1.0;
		gmtstat_Cdiv (z, v, tmp);
		gmtstat_Cmul (R,tmp,r);
		R[GMT_RE] = r[GMT_RE];	R[GMT_IM] = r[GMT_IM];
	}
	z[GMT_RE] = v[GMT_RE] + 1.0;
	tmp[GMT_RE] = 0.25;	tmp[GMT_IM] = 0.0;
	gmtstat_Cdiv (tmp, z, X);
	tmp[GMT_RE] = 0.35 + 6.1 * X[GMT_RE];	tmp[GMT_IM] = 6.1*X[GMT_IM];
	gmtstat_Cmul (X, tmp, z);
	z[GMT_RE] = 1.0 - 3.0*z[GMT_RE];	z[GMT_IM] = -3.0*z[GMT_IM];
	gmtstat_Cmul (X, z, tmp);
	G[GMT_RE] = 1.0 + 5.0 * tmp[GMT_RE];	G[GMT_IM] = 5.0 * tmp[GMT_IM];
	z[GMT_RE] = 8.0 * X[GMT_RE];	z[GMT_IM] = 8.0 * X[GMT_IM];
	M = sqrt(hypot(z[GMT_RE], z[GMT_IM]));
	L = 0.5 * atan2 (z[GMT_IM], z[GMT_RE]);
	tmp[GMT_RE] = M * cos(L);	tmp[GMT_IM] = M * sin(L);
	gmtstat_Cmul (G, X, z);
	z[GMT_RE] = 1.0 - 0.5*z[GMT_RE];	z[GMT_IM] = -0.5*z[GMT_IM];
	gmtstat_Cmul (X, z, r);
	r[GMT_RE] = 1.0 - r[GMT_RE];	r[GMT_IM] = -r[GMT_IM];
	gmtstat_Cmul (R, r, z);
	gmtstat_Cdiv (z, tmp, R);
	u[GMT_RE] = g[GMT_RE] = 2.0 * x;	u[GMT_IM] = g[GMT_IM] = f[GMT_IM] = t[GMT_IM] = 0.0;
	f[GMT_RE] = t[GMT_RE] = 1.0;
	k = 0.5;
	x2 = x * x;
	Xn = 1.0 + (1e8/(1 - x2));
	k1 = k + 1.0;
	fact = x2 / (k1*k1 - 0.25);
	t[GMT_RE] = (k*k - w[GMT_RE]) * fact;	t[GMT_IM] = -w[GMT_IM] * fact;
	k += 1.0;
	f[GMT_RE] += t[GMT_RE];	f[GMT_IM] += t[GMT_IM];
	k1 = k + 1.0;
	fact = u[GMT_RE] * x2 / (k1*k1 - 0.25);
	u[GMT_RE] = (k*k - w[GMT_RE]) * fact;	u[GMT_IM] = -w[GMT_IM] * fact;
	k += 1;
	g[GMT_RE] += u[GMT_RE];	g[GMT_IM] += u[GMT_IM];
	tmp[GMT_RE] = Xn * t[GMT_RE];	tmp[GMT_IM] = Xn * t[GMT_IM];
	while (k < K || gmtstat_Cabs (tmp) > gmtstat_Cabs(f)) {
		(*iter)++;
		k1 = k + 1.0;
		tmp[GMT_RE] = k*k - w[GMT_RE];	tmp[GMT_IM] = -w[GMT_IM];	fact = x2 / (k1*k1 - 0.25);
		gmtstat_Cmul (t, tmp, A);
		t[GMT_RE] = A[GMT_RE] * fact;	t[GMT_IM] = A[GMT_IM] * fact;
		k += 1.0;
		k1 = k + 1.0;
		f[GMT_RE] += t[GMT_RE];	f[GMT_IM] += t[GMT_IM];
		tmp[GMT_RE] = k*k - w[GMT_RE];	tmp[GMT_IM] = -w[GMT_IM];	fact = x2 / (k1*k1 - 0.25);
		gmtstat_Cmul (u, tmp, B);
		u[GMT_RE] = B[GMT_RE] * fact;	u[GMT_IM] = B[GMT_IM] * fact;
		k += 1.0;
		g[GMT_RE] += u[GMT_RE];	g[GMT_IM] += u[GMT_IM];
		tmp[GMT_RE] = Xn * t[GMT_RE];	tmp[GMT_IM] = Xn * t[GMT_IM];
	}
	fact = x2 / (1.0 - x2);
	f[GMT_RE] += t[GMT_RE] * fact;	f[GMT_IM] += t[GMT_IM] * fact;
	g[GMT_RE] += u[GMT_RE] * fact;	g[GMT_IM] += u[GMT_IM] * fact;
	if (!p_set) {
		gmtstat_Cmul(s,R,z);
		gmtstat_Cdiv(c,R,tmp);
		gmtstat_Cmul (g, z, A);	gmtstat_Cmul (f, tmp, B);
		pq[PV_RE] = (A[GMT_RE] + B[GMT_RE])/M_SQRT_PI;
		pq[PV_IM] = (A[GMT_IM] + B[GMT_IM])/M_SQRT_PI;
	}
	if (!q_set) {
		gmtstat_Cmul(c,R,z);
		gmtstat_Cdiv(s,R,tmp);
		gmtstat_Cmul (g, z, A);	gmtstat_Cmul (f, tmp, B);
		pq[QV_RE] = a[0]*M_SQRT_PI*(A[GMT_RE] - B[GMT_RE])/2.0;
		pq[QV_IM] = a[1]*M_SQRT_PI*(A[GMT_IM] - B[GMT_IM])/2.0;
	}
}

double gmt_grd_mean (struct GMT_CTRL *GMT, struct GMT_GRID *G, struct GMT_GRID *W) {
	/* Compute the [weighted] mean of a grid.  Handle geographic grids with spherical weights W [NULL for cartesian] */
	uint64_t node, n = 0;
	openmp_int row, col;
	double sum_zw = 0.0, sum_w = 0.0;
	if (W) {	/* Weights provided */
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node])) continue;
			sum_zw += G->data[node] * W->data[node];
			sum_w  += W->data[node];
			n++;
		}
	}
	else {	/* Plain average */
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node])) continue;
			sum_zw += G->data[node];
			n++;
		}
		sum_w = (double)n;
	}
	return (n == 0 || sum_w == 0.0) ? GMT->session.d_NaN : sum_zw / sum_w;
}

double gmt_grd_std (struct GMT_CTRL *GMT, struct GMT_GRID *G, struct GMT_GRID *W) {
	/* Compute the [weighted] std of a grid.  Handle geographic grids with spherical weights W [NULL for cartesian] */
	uint64_t node, n = 0;
	openmp_int row, col;
	double std, mean = 0.0, delta, sumw = 0.0;
	if (W) {	/* Weights provided */
		double temp, R, M2 = 0.0;
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node])) continue;
			temp  = W->data[node] + sumw;
			delta = G->data[node] - mean;
			R = delta * W->data[node] / temp;
			mean += R;
			M2 += sumw * delta * R;
			sumw = temp;
			n++;
		}
		std = (n <= 1 || sumw == 0.0) ? GMT->session.d_NaN : sqrt ((n * M2) / (sumw * (n - 1.0)));
	}
	else {	/* Plain average */
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node])) continue;
			n++;
			delta = G->data[node] - mean;
			mean += delta / n;
			sumw += delta * (G->data[node] - mean);
		}
		std = (n > 1) ? sqrt (sumw / (n - 1.0)) : GMT->session.d_NaN;
	}
	return (std);
}

double gmt_grd_rms (struct GMT_CTRL *GMT, struct GMT_GRID *G, struct GMT_GRID *W) {
	/* Compute the [weighted] rms of a grid.  Handle geographic grids with spherical weights W [NULL for cartesian] */
	uint64_t node, n = 0;
	openmp_int row, col;
	double rms, sum_z2w = 0.0, sum_w = 0.0;
	if (W) {	/* Weights provided */
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node])) continue;
			sum_z2w += W->data[node] * (G->data[node] * G->data[node]);
			sum_w   += W->data[node];
		}
	}
	else {	/* Plain average */
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node])) continue;
			n++;
			sum_z2w += (G->data[node] * G->data[node]);
		}
		sum_w = (double)n;
	}
	rms = (sum_w > 0) ? sqrt (sum_z2w / sum_w) : GMT->session.d_NaN;
	return (rms);
}

double gmt_grd_median (struct GMT_CTRL *GMT, struct GMT_GRID *G, struct GMT_GRID *W, bool overwrite) {
	/* Compute the weighted median of a grid.  Handle geographic grids with spherical weights W */
	/* Non-destructive: Original grid left as is unless overwrite = true */
	uint64_t node, n = 0;
	double wmed;

	if (W) {	/* Weights provided */
		openmp_int row, col;
		struct GMT_OBSERVATION *pair = gmt_M_memory (GMT, NULL, G->header->nm, struct GMT_OBSERVATION);
		if (pair == NULL) return 0.0;
		/* 1. Create array of value,weight pairs, skipping NaNs */
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node]))
				continue;
			pair[n].value    = G->data[node];
			pair[n++].weight = W->data[node];
		}
		/* 2. Find the weighted median */
		wmed = gmt_median_weighted (GMT, pair, n);
		gmt_M_free (GMT, pair);
	}
	else {	/* Plain median */
		struct GMT_GRID *Z = (overwrite) ? G : gmt_duplicate_grid (GMT, G, GMT_DUPLICATE_DATA);
		gmt_grd_pad_off (GMT, Z);	/* Undo pad if one existed so we can sort */
		gmt_sort_array (GMT, Z->data, Z->header->nm, GMT_FLOAT);
		for (n = Z->header->nm; n > 1 && gmt_M_is_fnan (Z->data[n-1]); n--);
		if (n)
			wmed = (n%2) ? Z->data[n/2] : 0.5f * (Z->data[(n-1)/2] + Z->data[n/2]);
		else
			wmed = GMT->session.f_NaN;
		if (!overwrite) gmt_free_grid (GMT, &Z, true);
	}
	return wmed;
}

double gmt_grd_mad (struct GMT_CTRL *GMT, struct GMT_GRID *G, struct GMT_GRID *W, double *median, bool overwrite) {
	/* Compute the [weighted] MAD of a grid.  Handle geographic grids with spherical weights W [NULL for cartesian].
	 * Non-destructive: Original grid left as is unless overwrite = true.
	 * If median == NULL then we must first compute the median, else we already have it */
	uint64_t node, n = 0;
	double wmed, wmad;
	if (W) {	/* Weights provided */
		openmp_int row, col;
		struct GMT_OBSERVATION *pair = gmt_M_memory (GMT, NULL, G->header->nm, struct GMT_OBSERVATION);
		if (pair == NULL) return 0.0;
		if (median) {	/* Already have the median */
			wmed = *median;
			/* 3. Compute the absolute deviations from this median */
			gmt_M_grd_loop (GMT, G, row, col, node) {
				if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node]))
					continue;
				pair[n].value    = (gmt_grdfloat)fabs (G->data[node] - wmed);
				pair[n++].weight = W->data[node];
			}
		}
		else {	/* Must first compute median */
			/* 1. Create array of value,weight pairs, skipping NaNs */
			gmt_M_grd_loop (GMT, G, row, col, node) {
				if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node]))
					continue;
				pair[n].value    = G->data[node];
				pair[n++].weight = W->data[node];
			}
			/* 2. Find the weighted median */
			wmed = gmt_median_weighted (GMT, pair, n);
			/* 3. Compute the absolute deviations from this median */
			for (node = 0; node < n; node++) pair[node].value = (gmt_grdfloat)fabs (pair[node].value - wmed);
		}
		/* 4. Find the weighted median absolute deviation */
		wmad = MAD_NORMALIZE * gmt_median_weighted (GMT, pair, n);
		gmt_M_free (GMT, pair);
	}
	else {	/* Plain MAD */
		struct GMT_GRID *Z = (overwrite) ? G : gmt_duplicate_grid (GMT, G, GMT_DUPLICATE_DATA);
		gmt_grd_pad_off (GMT, Z);	/* Undo pad if one existed so we can sort */
		if (median) {	/* Already have the median */
			wmed = *median;
			n = Z->header->nm;
		}
		else {	/* Must first compute the median */
			gmt_sort_array (GMT, Z->data, Z->header->nm, GMT_FLOAT);
			for (n = Z->header->nm; n > 1 && gmt_M_is_fnan (Z->data[n-1]); n--);
			if (n)
				wmed = (n%2) ? Z->data[n/2] : 0.5 * (Z->data[(n-1)/2] + Z->data[n/2]);
			else
				wmed = GMT->session.d_NaN;
		}
		gmt_getmad_f (GMT, Z->data, n, wmed, &wmad);
		if (!overwrite) gmt_free_grid (GMT, &Z, true);
	}
	return wmad;
}

double gmt_grd_mode (struct GMT_CTRL *GMT, struct GMT_GRID *G, struct GMT_GRID *W, bool overwrite) {
	/* Compute the weighted mode (lms) of a grid.  Handle geographic grids with spherical weights W */
	/* Non-destructive: Original grid left as is unless overwrite = true */
	uint64_t node, n = 0;
	double wmode;

	if (W) {	/* Weights provided */
		openmp_int row, col;
		struct GMT_OBSERVATION *pair = gmt_M_memory (GMT, NULL, G->header->nm, struct GMT_OBSERVATION);
		if (pair == NULL) return 0.0;
		/* 1. Create array of value,weight pairs, skipping NaNs */
		gmt_M_grd_loop (GMT, G, row, col, node) {
			if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node]))
				continue;
			pair[n].value    = G->data[node];
			pair[n++].weight = W->data[node];
		}
		/* 2. Find the weighted lms mode */
		wmode = (gmt_grdfloat)gmt_mode_weighted (GMT, pair, n);
		gmt_M_free (GMT, pair);
	}
	else {	/* Plain median */
		unsigned int gmt_mode_selection = 0, GMT_n_multiples = 0;
		struct GMT_GRID *Z = (overwrite) ? G : gmt_duplicate_grid (GMT, G, GMT_DUPLICATE_DATA);
		gmt_grd_pad_off (GMT, Z);	/* Undo pad if one existed so we can sort */
		gmt_sort_array (GMT, Z->data, Z->header->nm, GMT_FLOAT);
		for (n = Z->header->nm; n > 1 && gmt_M_is_fnan (Z->data[n-1]); n--);
		if (n)
			gmt_mode_f (GMT, Z->data, n, n/2, 0, gmt_mode_selection, &GMT_n_multiples, &wmode);
		else
			wmode = GMT->session.d_NaN;
		if (!overwrite) gmt_free_grid (GMT, &Z, true);
		if (GMT_n_multiples > 0) GMT_Report (GMT->parent, GMT_MSG_WARNING, "%d Multiple modes found in the grid\n", GMT_n_multiples);
	}
	return wmode;
}

double gmt_grd_lmsscl (struct GMT_CTRL *GMT, struct GMT_GRID *G, struct GMT_GRID *W, double *mode, bool overwrite) {
	/* Compute the [weighted] LMSSCL of a grid.  Handle geographic grids with spherical weights W [NULL for cartesian]
	 * Non-destructive: Original grid left as is unless overwrite = true.
	 * If mode == NULL then we must first compute the mode, else use this mode */
	uint64_t node, n = 0;
	double wmode, lmsscl;
	if (W) {	/* Weights provided */
		openmp_int row, col;
		struct GMT_OBSERVATION *pair = gmt_M_memory (GMT, NULL, G->header->nm, struct GMT_OBSERVATION);
		if (pair == NULL) return 0.0;
		if (mode) {	/* Already got the mode */
			wmode = *mode;
			/* 3. Compute the absolute deviations from this mode */
			gmt_M_grd_loop (GMT, G, row, col, node) {
				if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node]))
					continue;
				pair[n].value    = (gmt_grdfloat)fabs (G->data[node] - wmode);
				pair[n++].weight = W->data[node];
			}
		}
		else {	/* Must first find the mode */
			/* 1. Create array of value,weight pairs, skipping NaNs */
			gmt_M_grd_loop (GMT, G, row, col, node) {
				if (gmt_M_is_fnan (G->data[node]) || gmt_M_is_dnan (W->data[node]))
					continue;
				pair[n].value    = G->data[node];
				pair[n++].weight = W->data[node];
			}
			/* 2. Find the weighted median */
			wmode = (gmt_grdfloat)gmt_mode_weighted (GMT, pair, n);
			/* 3. Compute the absolute deviations from this mode */
			for (node = 0; node < n; node++) pair[node].value = (gmt_grdfloat)fabs (pair[node].value - wmode);
		}
		/* 4. Find the weighted median absolute deviation and scale it */
		lmsscl = MAD_NORMALIZE * gmt_median_weighted (GMT, pair, n);
		gmt_M_free (GMT, pair);
	}
	else {	/* Plain LMSSCL */
		unsigned int gmt_mode_selection = 0, GMT_n_multiples = 0;
		struct GMT_GRID *Z = (overwrite) ? G : gmt_duplicate_grid (GMT, G, GMT_DUPLICATE_DATA);
		gmt_grd_pad_off (GMT, Z);	/* Undo pad if one existed so we can sort */
		if (mode) {	/* Already got the mode */
			wmode = *mode;
			n = Z->header->nm;
		}
		else {/* First compute the mode */
			gmt_sort_array (GMT, Z->data, Z->header->nm, GMT_FLOAT);
			for (n = Z->header->nm; n > 1 && gmt_M_is_fnan (Z->data[n-1]); n--);
			if (n)
				gmt_mode_f (GMT, Z->data, n, n/2, 0, gmt_mode_selection, &GMT_n_multiples, &wmode);
			else
				wmode = GMT->session.d_NaN;
		}
		gmt_getmad_f (GMT, Z->data, n, wmode, &lmsscl);
		if (!overwrite) gmt_free_grid (GMT, &Z, true);
		if (GMT_n_multiples > 0) GMT_Report (GMT->parent, GMT_MSG_WARNING, "%d Multiple modes found in the grid\n", GMT_n_multiples);
	}
	return lmsscl;
}

GMT_LOCAL void gmtstat_get_geo_cellarea (struct GMT_CTRL *GMT, struct GMT_GRID *G) {
	/* Calculate geographic SPHERICAL area in km^2 and place in grid G.
	 * Integrating the area between two parallels +/- yinc/2 to either side of latitude y on a sphere
	 * and partition it amount all cells in longitude yields the exact area (angles in radians)
	 *     A(y) = 2 * R^2 * xinc * sin (0.5 * yinc) * cos(y)
	 * except at the points at the pole (gridline registration) or near the pole (pixel reg).
	 * There, the integration yields
	 *     A(pole) = R^2 * xinc * (1.0 - cos (f * yinc))
	 * where f = 0.5 for gridline-registered and f = 1 for pixel-registered grids.
	 * P.Wessel, July 2016.
	 */
	uint64_t node;
	openmp_int row, col, first_row = 0, last_row = (openmp_int)G->header->n_rows - 1, last_col = (openmp_int)G->header->n_columns - 1;
	unsigned int j, ltype;
	double lat, area, f, row_weight, col_weight = 1.0, R2 = pow (0.001 * GMT->current.proj.mean_radius, 2.0);	/* squared mean radius in km */
	char *aux[6] = {"geodetic", "authalic", "conformal", "meridional", "geocentric", "parametric"};
	char *rad[5] = {"mean (R_1)", "authalic (R_2)", "volumetric (R_3)", "meridional", "quadratic"};

	ltype = (GMT->current.setting.proj_aux_latitude == GMT_LATSWAP_NONE) ? 0 : 1+GMT->current.setting.proj_aux_latitude/2;
	GMT_Report (GMT->parent, GMT_MSG_INFORMATION, "Compute spherical gridnode areas using %s radius [R = %.12g km] and %s latitudes\n",
		rad[GMT->current.setting.proj_mean_radius], GMT->current.proj.mean_radius, aux[ltype]);
	/* May need special treatment of pole points */
	f = (G->header->registration == GMT_GRID_NODE_REG) ? 0.5 : 1.0;	/* Half pizza-slice for gridline regs with node at pole, full slice for grids */
	area = R2 * (G->header->inc[GMT_X] * D2R);
	if (doubleAlmostEqualZero (G->header->wesn[YHI], 90.0)) {	/* North pole row */
		row_weight = 1.0 - cosd (f * G->header->inc[GMT_Y]);
		gmt_M_col_loop (GMT, G, first_row, col, node) {
			if (G->header->registration == GMT_GRID_NODE_REG) col_weight = (col == 0 || col == last_col) ? 0.5 : 1.0;
			G->data[node] = (gmt_grdfloat)(row_weight * col_weight * area);
		}
		first_row++;
	}
	if (doubleAlmostEqualZero (G->header->wesn[YLO], -90.0)) {	/* South pole row */
		row_weight = 1.0 - cosd (f * G->header->inc[GMT_Y]);
		gmt_M_col_loop (GMT, G, last_row, col, node) {
			if (G->header->registration == GMT_GRID_NODE_REG) col_weight = (col == 0 || col == last_col) ? 0.5 : 1.0;
			G->data[node] = (gmt_grdfloat)(row_weight * col_weight * area);
		}
		last_row--;
	}
	/* Below we just use the standard graticule equation  */
	area *= 2.0 * sind (0.5 * G->header->inc[GMT_Y]);	/* Since no longer any special cases with poles below */
	for (row = first_row, j = first_row + G->header->pad[YHI]; row <= last_row; row++, j++) {
		lat = gmt_M_grd_row_to_y (GMT, row, G->header);
		lat = gmt_lat_swap (GMT, lat, GMT->current.setting.proj_aux_latitude);	/* Convert to selected auxiliary latitude */
		row_weight = cosd (lat);
		gmt_M_col_loop (GMT, G, row, col, node) {	/* Loop over cols; always save the next left before we update the array at that col */
			if (G->header->registration == GMT_GRID_NODE_REG) col_weight = (col == 0 || col == last_col) ? 0.5 : 1.0;
			G->data[node] = (gmt_grdfloat)(row_weight * col_weight * area);
		}
	}
}

GMT_LOCAL void gmtstat_get_cart_cellarea (struct GMT_CTRL *GMT, struct GMT_GRID *G) {
	/* Calculate Cartesian cell areas in user units */
	uint64_t node;
	openmp_int row, col, last_row = (openmp_int)G->header->n_rows - 1, last_col = (openmp_int)G->header->n_columns - 1;
	double row_weight = 1.0, col_weight = 1.0, area = G->header->inc[GMT_X] * G->header->inc[GMT_Y];	/* All whole cells have same area */
	gmt_M_unused(GMT);
	gmt_M_row_loop (GMT, G, row) {	/* Loop over the rows */
		if (G->header->registration == GMT_GRID_NODE_REG) row_weight = (row == 0 || row == last_row) ? 0.5 : 1.0;	/* half-cells in y */
		gmt_M_col_loop (GMT, G, row, col, node) {	/* Now loop over the columns */
			if (G->header->registration == GMT_GRID_NODE_REG) col_weight = (col == 0 || col == last_col) ? 0.5 : 1.0;	/* half-cells in x */
			G->data[node] = (gmt_grdfloat)(row_weight * col_weight * area);
		}
	}
}

void gmt_get_cellarea (struct GMT_CTRL *GMT, struct GMT_GRID *G) {
	/* Calculate geographic spherical in km^2 or plain Cartesian area in user_unit^2 and place in grid G. */
	if (gmt_M_is_geographic (GMT, GMT_IN))
		gmtstat_get_geo_cellarea (GMT, G);
	else
		gmtstat_get_cart_cellarea (GMT, G);
}

double gmt_von_mises_mu_and_kappa (struct GMT_CTRL *GMT, double *data, double *w, uint64_t n, double *kappa) {
	/* Return the mean and kappa for a von Mises fit to (possibly weighted) data.
	 * It is assumed that data have been scaled to 0-360. Weights w is possibly NULL for no weights */
	uint64_t k;
	double mean = 0.0, x_r = 0.0, y_r = 0.0, s_w = 0.0, ww = 1.0;
	double lo, hi, midval, range2, delta_R, s, c, R_bar;

	for (k = 0; k < n; k++) {
		if (gmt_M_is_dnan (data[k])) continue;
		if (w) ww = w[k];	/* Otherwise it is a constant 1 */
		sincosd (data[k], &s, &c);
		x_r += c * ww;	y_r += s * ww;
		s_w += ww;
	}
	if (s_w > 0.0) {	/* Can compute the statistics */
		x_r /= s_w;	y_r /= s_w;
		mean = atan2d (y_r, x_r);
	}
	else {	/* No data, basically */
		*kappa = GMT->session.d_NaN;
		return (GMT->session.d_NaN);
	}
	/* Here we have actual values */
	R_bar = hypot (x_r, y_r);
	if (R_bar >= 0.999) {	/* Just return a big kappa for R almost = 1 */
		*kappa = 500.0;	/* kappa = 500 gives R_bar = 0.998999916722 so close enough */
		return (mean);
	}
	/* Compute kappa by a dumb bisection search */
	lo = 0.0;	hi = 500.0;
	while (fabs (hi - lo) > GMT_CONV8_LIMIT) {
		midval = 0.5 * (hi + lo);
		range2 = 0.5 * (hi - lo);
		delta_R = (gmt_i1 (GMT, midval) / gmt_i0 (GMT, midval)) - R_bar;
		if (delta_R > GMT_CONV8_LIMIT)	/* Need a smaller R next time */
			hi -= range2;
		else if (delta_R < -GMT_CONV8_LIMIT)	/* Need a larger R next time */
			lo += range2;
		else 	/* Got it, set lo = hi to exit loop */
			lo = hi;
	}
	*kappa = midval;

	return (mean);
}

