matlab: filling matrix diagonalwise [duplicate]

Answer 1

 ix=bsxfun(@plus,[1:n],[n-1:-1:0]'); %generate indices
 A=a(ix);

or

 A=hankel(a) %might be faster than toeplitz because half the matrix is zero
 A(n:-1:1,1:n)

here is what hankel does internally (at least in ML R2013a), adapted to this problem:

c=[1:n];
r=[n-1:-1:0]';
idx=c(ones(n,1),:)+r(:,ones(n,1));
A=a(ix);

I guess the bsxfun solution and what thewaywewalk supposed is the fastest (it's basically the same)

Answer 2

Go with:

n = (numel(a)+1)/2;
A = a(bsxfun(@minus, n+1:n+n, (1:n).'));