计算这个矩阵的最有效方法是什么？

Question

I have a N-square matrix B of integers and i want to build the matrix A such that

A[m,n] = sum([B[i,j] for i in range(1,m) for j in range(1,n)])

As B can be quite big, computing A naively coefficient by coefficient takes much time.
What is the most effective way to compute A?

Answer 1

import numpy as np

A = np.cumsum(np.cumsum(a, axis=0), axis=1)

You're in luck. Two calls to numpy.cumsum (cumulative sum) should do the trick.

https://numpy.org/doc/stable/reference/generated/numpy.cumsum.html