Create a matrix by shifting a matrix column by column to

I have matrix 'a'. How can I create matrix 'b'?

Answer 1

[Walter Roberson]

b = zeros(9, 4);
for K = 1 : 3
   b((K-1)*3+1:K*3, K:K+1) = a;
end

Answer 2

[Andrei Bobrov]

b = kron(convmtx(a(1,:),3),ones(size(a,1),1));

or

s = size(a);
r = 2*s(2);
v = (1:s(1))';
b = kron(a0(rem((1:r) + flip(v),r)*s(1) + v),ones(s(1),1));