# Copyright (C) 2021 Intel Labs
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# ===============================================================================================
import torch
import torch.nn as nn
import torch.distributions as distributions


class BaseVariationalLayer_(nn.Module):
    def __init__(self):
        super().__init__()

    def kl_div(self, mu_q, sigma_q, mu_p, sigma_p):
        """
        Calculates kl divergence between two gaussians (Q || P)

        Parameters:
             * mu_q: torch.Tensor -> mu parameter of distribution Q
             * sigma_q: torch.Tensor -> sigma parameter of distribution Q
             * mu_p: float -> mu parameter of distribution P
             * sigma_p: float -> sigma parameter of distribution P

        returns torch.Tensor of shape 0
        """
        kl = torch.log(sigma_p) - torch.log(
            sigma_q) + (sigma_q**2 + (mu_q - mu_p)**2) / (2 *
                                                          (sigma_p**2)) - 0.5
        return kl.sum()
