defining diagonals in python

Question

How would I go about creating the matrix

[[ 1  2  0  0  0]
 [-1  1  2  0  0]
 [ 0 -1  1  2  0]
 [ 0  0 -1  1  2]
 [ 0  0  0 -1  1]]

using the numpy.diag() function in Python?

I want to define the main diagonal and also the parallel diagonals of the matrix.

matrix like this [1 2 0 0 0; -1 1 2 0 0; 0 -1 1 2 0; 0 0 -1 1 2; 0 0 0 -1 1] — Safoora Khosravi, Jan 26 '20 at 23:14
What 'matrix' type? That's not valid input or display for any common type. — hpaulj, Jan 27 '20 at 02:26
`scipy.sparse` has `diag` that let you specify several diagonals at once, but the `numpy` version(s) only does one at a time. But array addition is fast. — hpaulj, Jan 27 '20 at 05:50

score 1 · Answer 1 · answered Jan 27 '20 at 00:00

This should do it:

import numpy as np

subdiagonal = np.diag([-1,-1,-1,-1], -1)
diagonal = np.diag([1,1,1,1,1])
superdiagonal = np.diag([2,2,2,2], 1)

total = subdiagonal + diagonal + superdiagonal

print(total)

It gives this output:

[[ 1  2  0  0  0]
 [-1  1  2  0  0]
 [ 0 -1  1  2  0]
 [ 0  0 -1  1  2]
 [ 0  0  0 -1  1]]

defining diagonals in python

1 Answers1