Khatri-Rao product of a list of matrices
This can be seen as a column-wise kronecker product.
matrices : list of tensors
List of 2D tensors with the same number of columns, i.e.:
for i in len(matrices): matrices[i].shape = (n_i, m)
khatri_rao_product : tensor of shape
prod(n_i) = prod([m.shape for m in matrices])(i.e. the product of the number of rows of all the matrices in the product.)