Most efficient way to generate combinations

Dear all; I need to generate a large serie of combinations and it is taking a lot. I'm using 3 cycles one inside the other but I'm sure there's a better way to achieve this.

Here's what I'm currently doing:

indices=0; %indices matrix
l=1;
for i=1:200;
  for j=1:300;
      for k=1:250;
          indices(l,1)=i-1;
          indices(l,2)=j-1;
          indices(l,3)=k-1;
          l=l+1;
      end
  end
end

Please note that i, j and k have different lengths (thus values).

Any help would be greatly appreciated!

Thank you!

Answer 1

[Walter Roberson]

[I, J, K] = ndgrid(0:199, 0:299, 0:249);
indices = horzcat(I(:), J(:), K(:));

Answer 2

[Jonathan Sullivan]

You can use allcomb (which can be found here)

a = (1:200)-1;
b = (1:300)-1;
c = (1:250)-1;
indices = allcomb(a,b,c);

Answer 3

[Lorenzo]

Thank you both!

Eventually I did it with

[p,q,n] = meshgrid(1:length(x),1:length(y),1:length(z));

indices=[p(:)-1 q(:)-1 n(:)-1];