How can I sum only few values in a diagonal matrix?

13 views (last 30 days)
if I have a diagonal matrix, and I use sum(diag(A)) , it gives me the sum of entire diagonal, but I only want the sum of lets say 1st three values in the diagonal? How can I add them?
Thank you!!

Accepted Answer

Mischa Kim
Mischa Kim on 14 Apr 2014
Rida, use
sum(diag(A(1:3,1:3)))

More Answers (2)

Alberto
Alberto on 14 Apr 2014
Sum=0;
for k=1:3 % will sum 3 first diagonal elements Sum=Sum+A(k,k);
end
You can change the range k=1:3 with an array with the index of elements u want to sum.

Walter Roberson
Walter Roberson on 26 Mar 2018
Without a loop:
r = size(A, 1);
sum(A([1, r+1, 2*(r+1)]))

Categories

Find more on Operating on Diagonal Matrices in Help Center and File Exchange

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!