Python 3d array times 1d vector

Question

I'm trying to multiply a [12x256x256] array with a [12] array. The idea is taht the first one is a stack of 12 [256x256] arrays and the 2nd one is a stack of 1d scalars. So if the 2nd array is [1,2,3,4,...,12], then I want to multiply the first layer of the 3d one by 1, the 2nd layer by 2, etc.

How can I do this?

01zhou · Accepted Answer · 2014-06-10 18:41:00Z

3

You can add new axises and multiply them.

import numpy as np    
a = np.ones((12,256,256))
b = np.array(range(12))+1
c = a * b[:, np.newaxis, np.newaxis]

answered Jun 10, 2014 at 18:41

01zhou

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Fabricator · Accepted Answer · 2014-06-10 18:39:38Z

0

In numpy you can do

# let m be 12x256x256, n be 12
m = np.array(m)
n = np.array(n)
(m.swapaxes(0,2) * n).swapaxes(2,0)

answered Jun 10, 2014 at 18:39

Fabricator

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