# This file is part of idtracker.ai a multiple animals tracking system
# described in [1].
# Copyright (C) 2017- Francisco Romero Ferrero, Mattia G. Bergomi,
# Francisco J.H. Heras, Robert Hinz, Gonzalo G. de Polavieja and the
# Champalimaud Foundation.
#
# idtracker.ai is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) 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 General Public License for more details. In addition, we require
# derivatives or applications to acknowledge the authors by citing [1].
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
#
# For more information please send an email (idtrackerai@gmail.com) or
# use the tools available at https://gitlab.com/polavieja_lab/idtrackerai.git.
#
# [1] Romero-Ferrero, F., Bergomi, M.G., Hinz, R.C., Heras, F.J.H.,
# de Polavieja, G.G., Nature Methods, 2019.
# idtracker.ai: tracking all individuals in small or large collectives of
# unmarked animals.
# (F.R.-F. and M.G.B. contributed equally to this work.
# Correspondence should be addressed to G.G.d.P:
# gonzalo.polavieja@neuro.fchampalimaud.org)
from torch import nn

eps = 1e-7  # Avoid calculating log(0). Use the small value of float16. It also works fine using 1e-35 (float32).


class KLDiv(nn.Module):
    # Calculate KL-Divergence

    def forward(self, predict, target):
        assert predict.ndimension() == 2, "Input dimension must be 2"
        target = target.detach()

        # KL(T||I) = \sum T(logT-logI)
        predict += eps
        target += eps
        logI = predict.log()
        logT = target.log()
        TlogTdI = target * (logT - logI)
        kld = TlogTdI.sum(1)
        return kld
