Creating combination matrix of all combinations

Hi,

I've two or more variable and i've to form a combination matrix out of it. For example,

I've 2 variables say a=[1,2,3,4];b=[5,6,7,8];

now I've to form the combinations of their operation,Like

out=[];

for i=1:length(a)

for j=1:length(b)

out(end+1,1:2)=[a(i),b(j)];

end

end

But the above program works for only 2 variables. How to write a code which works for nay number of variables?

Answer 1

[Guillaume]

Use ndgrid and expansion of cell arrays into comma-separated lists :

function c = cartprod(varargin)
    %c = allcomb(v1, v2, ....)  create a matrix of the cartesian product of all vector
    %v1, v2,... must be numeric vectors
    %c(r, :) is a unique combination of the elements of v1, v2, ...
    %c is size numel(v1)*numel(v2)*... x N (N: number of input vectors).
    %TODO: add input validation
    c = cell(size(varargin));  %create cell array to store output of ndgrid
    [c{:}] = ndgrid(varargin{:});  %expand varargin into c-s-l and store output in c. C{i} is N-d array (N = number of vectors)
    c = cat(numel(varargin) + 1, c{:});  %concatenate the N-d arrays into a N+1-d array
    c = reshape(c, [], numel(varargin));  %and reshape into ?xN matrix
end