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Create a matrix with same diagonal elements

Asked by Grzegorz Lippe on 27 Nov 2013
Latest activity Commented on by Grzegorz Lippe on 27 Nov 2013
Hello World,
I have a vector
x = [x_1 x_2 x_3]
and would like to create a Matrix which looks like this:
X = [x_1 0 0
x_2 x_1 0
x_3 x_2 x_1]
Is there a loop-less way or a Matlab function to do this? The best thing I could come up with is:
x = 1:3 ;
N = length(x) ;
X = zeros(N) ;
for kk=1:N
X(kk:N+1:end) = x(kk) ;
end
X = tril(X)

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2 Answers

Answer by Azzi Abdelmalek
on 27 Nov 2013
Edited by Azzi Abdelmalek
on 27 Nov 2013
 Accepted Answer

X=[10 20 30]
n=numel(X);
out=tril(cell2mat(arrayfun(@(x) circshift(X',[x 0]),0:n-1,'un',0)))

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Answer by Andrei Bobrov
on 27 Nov 2013

out = tril(toeplitz(x));

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