How to construct this vector without loop?

Hi, everyone:

I was wondering, is it possible to construct following vector without for loop?

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

or equivalently A=[1:(3*1), 1:(3*2), 1:(3*3), 1:(3*4), ...., 1:(3*n)]

Many thanks!

Answer 1

[Jos (10584)]

Here is flexible version not using cell2mat:

n = 4 ; % user specified
V = 3 ; % as in the example -> [1:V 1:2*V ... 1:n*V]

ix = V*[1:n]
A = ones(1,sum(ix))
ix =ix(1:n-1)
A(cumsum(ix)+1)=-ix+1
A = cumsum(A) % result

Answer 2

[Azzi Abdelmalek]

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

Answer 3

[Vivek Selvam]

vec = 3*(1:n);
A   = cell2mat(arrayfun(@(x) 1:x,vec,'UniformOutput',0));

or

vec = 1:n;
A   = cell2mat(arrayfun(@(x) 1:3*x,vec,'UniformOutput',0));