matrix – Mapping Expression – Code Review Stack Exchange

I have the following code, for constructing a matrix of multiples of 4:

import numpy as np
width, height = 4, 4

vector = np.zeros (width * height)
for i in the range (1, width * height):
vector[i] = vector[i-1] 4

matrix = vector.reshape ((width, height))
matrix

>>> table ([[ 0.,  4.,  8., 12.],
           [16., 20., 24., 28.],
           [32., 36., 40., 44.],
           [48., 52., 56., 60.]])

I'm looking for a line of code that gives some coordinates [x, y] from the matrix above directly returns me the values, that is, for coordinates [0,0] I want 0, for coordinates [1,1] I want 20.

My problem is that my width and height values ​​can be extremely large and that I only need the value of a few positions. Not all. I know this should be possible in an expression involving width, height, and x and y coordinates. Something like: width times x position plus 4 …

Thank you for your time.