# How to make Triu in reverse axis for triangular matrices ?

2 views (last 30 days)
Ramesh Bala on 2 Dec 2020
Commented: Ramesh Bala on 2 Dec 2020
The function triu makes the upper triangular matrix in the shape of L . How shall I reverse it like to make it run in opposite diirection.
The below function make triu in the top to bottom,i wanna to make it bottom to top and thus reversing it ?
A = ones(6);
idx = ( A(:,3:end) );
A(:,3:end) = triu(idx,-1)

John D'Errico on 2 Dec 2020
Are you asking to do no more than this?
A = magic(6)
A = 6×6
35 1 6 26 19 24 3 32 7 21 23 25 31 9 2 22 27 20 8 28 33 17 10 15 30 5 34 12 14 16 4 36 29 13 18 11
A = flip(tril(flip(A)))
A = 6×6
35 1 6 26 19 24 3 32 7 21 23 0 31 9 2 22 0 0 8 28 33 0 0 0 30 5 0 0 0 0 4 0 0 0 0 0
That is a simple way to do it. There would be others.
Ramesh Bala on 2 Dec 2020
THis is what I was looking for and it worked :)

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