# Copyright (c) 2018, Curious AI Ltd. All rights reserved.
#
# This work is licensed under the Creative Commons Attribution-NonCommercial
# 4.0 International License. To view a copy of this license, visit
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# Creative Commons, PO Box 1866, Mountain View, CA 94042, USA.

"""Custom loss functions"""

import torch
from torch.nn import functional as F
from torch.autograd import Variable


def softmax_mse_loss(input_logits, target_logits):
    """Takes softmax on both sides and returns MSE loss

    Note:
    - Returns the sum over all examples. Divide by the batch size afterwards
      if you want the mean.
    - Sends gradients to inputs but not the targets.
    """
    assert input_logits.size() == target_logits.size()
    input_softmax = F.softmax(input_logits, dim=1)
    target_softmax = F.softmax(target_logits, dim=1)
    num_classes = input_logits.size()[1]
    return F.mse_loss(input_softmax, target_softmax, size_average=False) / num_classes


def softmax_kl_loss(input_logits, target_logits):
    """Takes softmax on both sides and returns KL divergence

    Note:
    - Returns the sum over all examples. Divide by the batch size afterwards
      if you want the mean.
    - Sends gradients to inputs but not the targets.
    """
    assert input_logits.size() == target_logits.size()
    input_log_softmax = F.log_softmax(input_logits, dim=1)
    target_softmax = F.softmax(target_logits, dim=1)
    return F.kl_div(input_log_softmax, target_softmax, size_average=False)


def symmetric_mse_loss(input1, input2):
    """Like F.mse_loss but sends gradients to both directions

    Note:
    - Returns the sum over all examples. Divide by the batch size afterwards
      if you want the mean.
    - Sends gradients to both input1 and input2.
    """
    assert input1.size() == input2.size()
    num_classes = input1.size()[1]
    return torch.sum((input1 - input2)**2) / num_classes
