Convolution along one axis only

Question

I have two 2-D arrays with the same first axis dimensions. In python, I would like to convolve the two matrices along the second axis only. I would like to get C below without computing the convolution along the first axis as well.

import numpy as np
import scipy.signal as sg

M, N, P = 4, 10, 20
A = np.random.randn(M, N)
B = np.random.randn(M, P)

C = sg.convolve(A, B, 'full')[(2*M-1)/2]

Is there a fast way?

Answer 1

You can use np.apply_along_axis to apply np.convolve along the desired axis. Here is an example of applying a boxcar filter to a 2d array:

import numpy as np

a = np.arange(10)
a = np.vstack((a,a)).T

filt = np.ones(3)

np.apply_along_axis(lambda m: np.convolve(m, filt, mode='full'), axis=0, arr=a)

This is an easy way to generalize many functions that don't have an axis argument.