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pythonnumpymatrix
TMOTTM
TMOTTM

Reputation: 3381

How to multiply diagonal elements by each other using numpy?

For the purpose of this exercise, let's consider a matrix where the element m_{i, j} is given by the rule m_{i, j} = i*j if i == j and 0 else.

Is there an easy "numpy" way of calculating such a matrix without having to resort to if statements checking for the indices?

Upvotes: 0

Views: 2808

Answers (3)

Vlad
Vlad

Reputation: 8585

Assuming you have a squared matrix, you can do this:

import numpy as np

ary = np.zeros((4, 4))
_ = [ary.__setitem__((i, i), i**2) for i in range(ary.shape[0])]
print(ary)
# array([[0., 0., 0., 0.],
#        [0., 1., 0., 0.],
#        [0., 0., 4., 0.],
#        [0., 0., 0., 9.]])

Upvotes: 0

FiercestJim
FiercestJim

Reputation: 308

You could use the identity matrix given by numpy.identity(n) and then multiply it by a n dimensional vector.

Upvotes: 0

BurnNote
BurnNote

Reputation: 436

You can use the numpy function diag to construct a diagonal matrix if you give it the intended diagonal as a 1D array as input.

So you just need to create that, like [i**2 for i in range (N)] with N the dimension of the matrix.

Upvotes: 1

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