Matlab: compute the sum of elements in the lower portion of a matrix

Question

I have to develop a Matlab function that computes the sum of the elements in the reverse diagonal, and the elements to the right of the reverse diagonal. Sum (A) = 38 ; Sum (B) = 40; Sum (C) = 25;

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Can somebody provide me a solution on how to go about using looping to solve this problem ?

Answer 1

For an×m Matrix:

1. Set the sum to 0, column to 1 and top to n (assuming (n,1) is the bottom-left corner of the matrix)

2. Add to the sum all elements in current column which row number is more or equal to the top .

3. Add 1 to column . If column is greater than m we are done.

4. Subtract 1 from top . If top is 0 , set top to 1 .

5. Go to 1.

Answer 2

对于矩阵M

Mysum = sum(sum(tril(rot90(M,-1))))