code: def forward_tensor(self, x):
          
          fwd = vec_to_tri(x, self.N)
          return tf.squeeze(fwd, axis=0) if self.squeeze else fwd
docs: 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