Transforms from the packed to unpacked representations (tf.tensors)
        
        :param x: packed tensor. Must have shape `self.num_matrices x triangular_number
        :return: Reconstructed tensor y of shape self.num_matrices x N x N

def forward_tensor(self, x):
        """
        Transforms from the packed to unpacked representations (tf.tensors)
        
        :param x: packed tensor. Must have shape `self.num_matrices x triangular_number
        :return: Reconstructed tensor y of shape self.num_matrices x N x N
        """
        fwd = vec_to_tri(x, self.N)
        return tf.squeeze(fwd, axis=0) if self.squeeze else fwd