Create lower triangular matrix from a vector in python-CodePudding

I want to create a python program which computes a matrix from a vector with some coefficients. So lets say we have the following vector of coefficients c = [c0, c1, c2] = [0, 1, 0], then I want to compute the matrix:

So how do I go from the vector c to creating a lower triangular matrix A. I know how to index it manually, but I need a program that can do it. I was maybe thinking about a for-loop inside another for-loop but I struggle with how it is done practically, what do you guys think should be done here?

CodePudding user response：

One way (assuming you're using plain arrays and not numpy or anything):

src = [0, 1, 0]
dst = [
    [ 
        src[i-j] if i >= j else 0
        for j in range(len(src))
    ] for i in range(len(src))
]

CodePudding user response：

You can try the following:

import numpy as np

c = [1, 2, 3, 4, 5]
n = len(c)
a = np.zeros((n,n))
for i in range(n):
    np.fill_diagonal(a[i:, :], c[i])
    
print(a)

It gives:

[[1. 0. 0. 0. 0.]
 [2. 1. 0. 0. 0.]
 [3. 2. 1. 0. 0.]
 [4. 3. 2. 1. 0.]
 [5. 4. 3. 2. 1.]]