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matlabtriangular

Get upper triangle in Matlab

I want to get the upper triangle from a matrix. MATLAB have the functions tril and triu, unfortunately they give the wrong triangle. I'm looking for following triangle, is there a command for it or must it be a loop? If so, how does it look?

test=[1 1 1; 1 1 0; 1 0 0];
Solution

  • You need to do it manually. There are several approaches:

    1. Use flipud to flip vertically before and after applying tril:

      M = magic(3); % example matrix
result = flipud(tril(flipud(M)));

    2. Use bsxfun to create the appropriate mask:

      M = magic(3); % example matrix
result = M .* (bsxfun(@plus, (1:size(M,1)).', 1:size(M,2)) <= size(M,1)+1);

    Any of the above gives

    >> M
M =
     8     1     6
     3     5     7
     4     9     2
>> result
result =
     8     1     6
     3     5     0
     4     0     0