Python: multiplying fixed array by element wise second array

Question

Example code:

import numpy as np
a = np.arange(1,11)
b = np.arange(1,11)
b[:] = 0
b[3] = 10
b[4] = 10
print(a, b)
[ 1  2  3  4  5  6  7  8  9 10] [ 0  0  0 10 10  0  0  0  0  0]

I am attempting to multiply b by element-wise a-array such that my resulting array is the following:

[0 0 10 30 50 70 90 110 130 150]

Any help would be greatly appreciated.

If what you mean is Hadamard product: en.wikipedia.org/wiki/Hadamard_product_(matrices) then you get it simply using a * b. However, for your values of a and b, the product is [ 0, 0, 0, 40, 50, 0, 0, 0, 0, 0] rather than whay you specified as expected output, so I think clarification is needed. — Błotosmętek
– Błotosmętek, Commented Mar 29, 2020 at 20:20

yatu · Accepted Answer · 2020-03-29 20:30:19Z

1

It looks like you want the convolution of both arrays:

np.convolve(a,b)[:len(a)+1]
# array([  0,   0,   0,  10,  30,  50,  70,  90, 110, 130, 150])

edited Mar 29, 2020 at 20:30

answered Mar 29, 2020 at 20:24

yatu

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1 Comment

MountainHorn Over a year ago

This is correct. I was mistaken on element wise multiplication. Thank you @yatu.

Shreya Kapoor · Accepted Answer · 2020-03-29 20:22:20Z

0

Elementwise multiplication of b with a shall give you [0,0,40,50,0,0,0,0,0,0] and not what you have stated.

answered Mar 29, 2020 at 20:22

Shreya Kapoor

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1 Comment

MountainHorn Over a year ago

Yes, I was mistaken. Solution to my problem solved above using np.convolve. Thank you for responding.

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