vgp.py 文件源码

def _build_likelihood(self):
        """
        This method computes the variational lower bound on the likelihood,
        which is:

            E_{q(F)} [ \log p(Y|F) ] - KL[ q(F) || p(F)]

        with

            q(\\mathbf f) = N(\\mathbf f \\,|\\, \\boldsymbol \\mu, \\boldsymbol \\Sigma)

        """

        # Get prior KL.
        KL = gauss_kl(self.q_mu, self.q_sqrt)

        # Get conditionals
        K = self.kern.K(self.X) + tf.eye(self.num_data, dtype=settings.float_type) * \
            settings.numerics.jitter_level
        L = tf.cholesky(K)

        fmean = tf.matmul(L, self.q_mu) + self.mean_function(self.X)  # NN,ND->ND

        q_sqrt_dnn = tf.matrix_band_part(tf.transpose(self.q_sqrt, [2, 0, 1]), -1, 0)  # D x N x N

        L_tiled = tf.tile(tf.expand_dims(L, 0), tf.stack([self.num_latent, 1, 1]))

        LTA = tf.matmul(L_tiled, q_sqrt_dnn)  # D x N x N
        fvar = tf.reduce_sum(tf.square(LTA), 2)

        fvar = tf.transpose(fvar)

        # Get variational expectations.
        var_exp = self.likelihood.variational_expectations(fmean, fvar, self.Y)

        return tf.reduce_sum(var_exp) - KL