Method _FPropSoftmax

Computes cross-entropy loss given the softmax input, labels and weights. Args: theta: A `.NestedMap` object containing weights' values of this layer and its children layers. softmax_input: A tensor of shape [time, batch, p.softmax.input_dim]. target_labels: A matrix of

(self,
                    theta,
                    softmax_input,
                    target_labels,
                    target_weights,
                    target_paddings,
                    target_segment_ids=None,
                    time_axis=0)