inst_b = tf.constant([[[1.5, 2.5, 3.5, 4.5], [5.5, 6.5, 7.5, 8.5],
                           [-1, -1, -1, -1], [-1, -1, -1, -1]],
                          [[-1, -1, -1, -1], [-1, -1, -1, -1],
                           [5.5, 6.5, 7.5, 8.5], [8.5, 7.5, 6.5, 5.5]],
                          [[1.5, 2.5, 3.5, 4.5], [4.5, 3.5, 2.5, 1.5],