"Kronecker" of varying dimensions?

Hi, I have a matrix A of dimension m x n and a vector b of natural numbers with dimension m x 1. I want to obtain a matrix C of dimension (b(1)+...+b(m)) x n by vertically stacking each A(i,:) b(i) times. For example:

A=[1 2 3; 4 5 6; 7 8 9];
b=[2; 1; 4];

I want to obtain

C=[1 2 3; 1 2 3; 4 5 6; 7 8 9; 7 8 9; 7 8 9; 7 8 9];

I cannot use loops.

Answer 1

[Azzi Abdelmalek]

A=[1 2 3; 4 5 6; 7 8 9] 
b=[2; 1; 4] 
out=cell2mat(arrayfun(@(x) repmat(A(x,:),b(x),1),(1:size(A,1))','un',0))