MATLAB: Create a matrix with same diagonal elements

Question

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)

Answer 1

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