I am playing around with tf.tensordot in Tensorflow. However, I am experiencing some inconsistencies which are bugging me. Below is a reproducible example:

tf.reset_default_graph()
tf.set_random_seed(42)
np.random.seed(42)
X = np.random.rand(150, 196, 268).astype(np.float32)
W = tf.Variable(initial_value=tf.random_normal([268, 22], stddev=0.1))
dotted_150 = tf.tensordot(X, W, axes=[[2], [0]])
with tf.Session() as sess:
    sess.run(tf.global_variables_initializer())
    output_150 = sess.run(dotted_150)

This returns a tensor that has dimensions (150, 196, 22)

tf.reset_default_graph()
tf.set_random_seed(42)
np.random.seed(42)
X = np.random.rand(1, 196, 268).astype(np.float32)
W = tf.Variable(initial_value=tf.random_normal([268, 22], stddev=0.1))
dotted_1 = tf.tensordot(X, W, axes=[[2], [0]])
with tf.Session() as sess:
    sess.run(tf.global_variables_initializer())
    output_1 = sess.run(dotted_1)

This returns a tensor that has dimensions (1, 196, 22)

Now, if we test whether the first element from output_150 is almost equal to the first and only element from output_1, the result is a mismatch between the two arrays.

np.testing.assert_allclose(output_1[0], output_150[0])

On the other hand, if we do:

np.random.seed(42)
input_150 = np.random.rand(150, 196, 268).astype(np.float32)
np.random.seed(42)
input_1 = np.random.rand(1, 196, 268).astype(np.float32)
np.testing.assert_equal(input_150[0], input_1[0])

We see that the inputs are exactly the same. With that said, I would expect that the outputs from the tf.tensordot to be the same as well and they are not.


On the same note, here is a tf.tensordot equivalent using tf.reshape and tf.matmul:

tf.reset_default_graph()
tf.set_random_seed(42)
np.random.seed(42)
X = np.random.rand(150, 196, 268).astype(np.float32)
W = tf.Variable(initial_value=tf.random_normal([268, 22], stddev=0.1))
reshaped = tf.reshape(X, [-1, 268])
mulled_150 = tf.reshape(tf.matmul(reshaped, W), [-1, 196, 22])
with tf.Session() as sess:
    sess.run(tf.global_variables_initializer())
    output_150 = sess.run(mulled_150)


tf.reset_default_graph()
tf.set_random_seed(42)
np.random.seed(42)
X = np.random.rand(1, 196, 268).astype(np.float32)
W = tf.Variable(initial_value=tf.random_normal([268, 22], stddev=0.1))
reshaped = tf.reshape(X, [-1, 268])
mulled_1 = tf.reshape(tf.matmul(reshaped, W), [-1, 196, 22])
with tf.Session() as sess:
    sess.run(tf.global_variables_initializer())
    output_1 = sess.run(mulled_1)

np.testing.assert_allclose(output_1[0], output_150[0])

The outcome is exactly the same, a mismatch between the output arrays. How can that be?

1 Answers

0
gorjan On Best Solutions

Apparently, if I use tf.float64 precision instead of tf.float32 the results are identical.