Tensorflow - matmul of input matrix with batch data

Question

I have some data represented by input_x. It is a tensor of unknown size (should be inputted by batch) and each item there is of size n. input

Answer 1

The matmul operation only works on matrices (2D tensors). Here are two main approaches to do this, both assume that U is a 2D tensor.

1. Slice embed into 2D tensors and multiply each of them with U individually. This is probably easiest to do using tf.scan() like this:

   h = tf.scan(lambda a, x: tf.matmul(x, U), embed)
   

2. On the other hand if efficiency is important it may be better to reshape embed to be a 2D tensor so the multiplication can be done with a single matmul like this:

   embed = tf.reshape(embed, [-1, m])
   h = tf.matmul(embed, U)
   h = tf.reshape(h, [-1, n, c])
   

   where c is the number of columns in U. The last reshape will make sure that h is a 3D tensor where the 0th dimension corresponds to the batch just like the original x_input and embed.