How to create triangle inside matrix?

What if I wanted a triangle of numbers from the formula (2n-1) that resulted in a triangle inside a matrix such that...

[0 0 0 0 1 0 0 0 0]
 0 0 0 2 1 2 0 0 0
 0 0 3 2 1 2 3 0 0
 0 4 3 2 1 2 3 4 0]

etc?...

Answer 1

[Andrei Bobrov]

sort(spdiags(toeplitz(1:n)))

[Billy Albritton]

Stop being a genius. :-)

[Billy Albritton]

What if I want to write a loop script to do the same thing?

[Andrei Bobrov]

Hi Billy!

With loop:

a = zeros(n,2*n-1);
for jj = 1:n
    a(jj,n-jj+1:n+jj-1) = [jj:-1:1,2:jj];
end

[Billy Albritton]

Thank you! You are amazing!