Instance, 038: the sum of the diagonal matrix

Title: Find the sum of the main diagonal elements of a 3*3 matrix.

Program Analysis: i and j are the same on the main diagonal

Code:

mat = [[1, 2, 3],[3, 4, 5],[4, 5, 6]]res = 0for i in range(len(mat)):print(i, i, ':', mat[i][i])res += mat[i][i]print('The main diagonal sum is: ', res)

Results:

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