multiply multidimensional arrays in python

Question

I have stored a number of 2d arrays in a 3d array and I need to multiply each one with a vector. so I have stored all those vectors in a 2d array. It's like this:

A = np.random.random((L, M, N))
B = np.random.random((L, M))

and I need to multiply each A[l] by B[l] which results in a Nx1 array and the output of the whole operation would be a LxN 2d array. Is there a function that can do this or do I need a loop?

A[l] is the l-th of those 2d arrays which is a MxN array and l is an integer between 0 and L-1. Likewise B[l] is a 1D array of length M. and I want to multiply transpose of A[l] into B[l]. — soroosh.strife
– soroosh.strife, Commented May 7, 2014 at 21:21
Ok, and how is the multiplication of the 1D array with the 2D array defined? — user3413108
– user3413108, Commented May 7, 2014 at 21:23
Normall matrix multiplication. I want to multiply transpose of A[l] which would be NxM into B[l] which would be Mx1 and get a Nx1 array — soroosh.strife
– soroosh.strife, Commented May 7, 2014 at 21:26

Newskooler · Accepted Answer · 2018-12-10 18:27:04Z

3

An option is np.einsum

import numpy as np
output = np.einsum("ijk, ij -> ik", A, B)

This results in a (L, N) sized array containing matrix products of all the A[i].T.dot(B[i])

edited Dec 10, 2018 at 18:27

Newskooler

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answered May 7, 2014 at 21:24

eickenberg

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1 Comment

eickenberg Over a year ago

You're welcome. It is worthwhile taking a look at the docs of np.einsum. This function is extremely versatile.

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