how to get sum of elements of lower right triangular matrix.? i have tried this one, can anyone please correct this one

Question

vamshidhar Reddy Peruvala 2016-12-2

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回答： Ibrahim Abouemira 2019-5-19

采纳的回答： Andrei Bobrov

在 MATLAB Online 中打开

function [sum] = halfsum( a )

[m, n]=size(a); sum=0;

for i= m:-1:1

    for j=n:-1:1
        if i==j || j<=i
            sum=sum+a(i,j);
        end
    end
end
end

output: halfsum([1 2 3;4 5 6;7 8 9])

ans =

34

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Answer 1

Andrei Bobrov 2016-12-2

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在 MATLAB Online 中打开

out = sum(a(rot90(tril(ones(size(a))),1)>0));

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Answer 2

Image Analyst 2016-12-2

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在 MATLAB Online 中打开

Don't use sum() as the name of your variable! You're destroying a built-in function. I wish we could make this a sticky on the forum because it happens so often, probably more often than people confusing (row,column) with (x,y).

Use tril and fliplr like this:

m = magic(9)  % Sample matrix.
lowerRight = fliplr(tril(fliplr(m)))
theSum = sum(lowerRight(:))

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vamshidhar Reddy Peruvala 2016-12-4

编辑：vamshidhar Reddy Peruvala 2016-12-4

if possible can you please correct my code in "for loop" ..?

Image Analyst 2016-12-4

The j loop should start at i, not n. And use theSum instead of sum. And the "if" is unnecessary.

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Answer 3

Ibrahim Abouemira 2019-5-19

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Hello,

Here's a proposed answer to your question.

The function takes as input at the most two-dimensional array. It computes the sum of the elements of that are in the lower right triangular part(counter-diagonal elements).

For example, if the input is [1 2; 3 4; 5 6; 7 8], then the function would return 21.

https://www.mathworks.com/matlabcentral/fileexchange/71592-sum-of-array-s-elements-in-the-lower-right-triangular-part