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

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vamshidhar Reddy Peruvala
回答： Ibrahim Abouemira 2019-5-19
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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采纳的回答

Andrei Bobrov
Andrei Bobrov 2016-12-2
out = sum(a(rot90(tril(ones(size(a))),1)>0));

更多回答（2 个）

Image Analyst
Image Analyst 2016-12-2
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(:))
Ibrahim Abouemira
Ibrahim Abouemira 2019-5-19
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

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