help in adding a descending order a symetric matric

Hello! I want to put in a descending order just the part upper the main diagonal in a symmetric matrix and to get the index of those elements. What should I change in this code?

function [values,i,j] = max(A,n)
[a, linIdx] = sort(A(:),'descend');
values = a(1:n);
[i,j] = ind2sub(size(A),linIdx(1:n));

[Walter Roberson]

Please do not call your function "max" as that interferes with using the key MATLAB routine "max"

Answer 1

[John Chilleri]

Hello,

Here's a very inelegant solution, but it does the job. I'm making all values below the main diagonal -Inf so that they're guaranteed to not be apart of the a(1:n) when you sort, assuming your original matrix does not contain -Infinities (this also includes the main diagonal, I can change it to exclude it if necessary).

function [values,i,j] = whateveryouwanttocallit(A,n) 
   low = tril(A-Inf,-1)+1;
   A = low.*A;
   [a, linIdx] = sort(A(:),'descend');
   values = a(1:n);
   [i,j] = ind2sub(size(A),linIdx(1:n));
end

Hope this helps!

Answer 2

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/newsreader/view_thread/278808 for information on extracting the upper diagonal.

However, the question arises of which index you are looking for. Are you looking for an index relative to the vector of extracted values, or are you looking for the index into the original matrix?

[ana take]

index into the original matrix