if in while loop not working - write combinations with unique proportions from input matrix to new matrix

I want to add the RGB-combinations (row in matrix P) with unique proportions (gcd=1) as a new row at the bottom of matrix Q. The code I have now (see below) isn't working though. Matlab doesn't create a new matrix Q.

N = 4;
R = 0:1:2^N-1;
R = transpose(R);
G = R;
B = R;
P = allcomb(R,G,B);
[m,n] = size(P);
i = 1;
  while i <= m
    i = i+1;
    if gcd(P(i,1),gcd(P(i,2),P(i,3))) == 1
      Q(end,:) = P(i,:);
  end

[dpb]

A) IS there an existant Q? If so, it must have been created prior to the above code snippet.

B) If Q does exist, then

Q(end,:) = ...

replaces the last row in it rather than augmenting it. Write either

Q(end+1,:) = RHS;

or

Q=[Q; RHS];

[Kid]

Already fixed the problem with the help of someone on another forum, the code is now:

N = 5;
R = 0:1:2^N-1;
R = transpose(R);
G = R;
B = R;
P = allcomb(R,G,B);
Q = [];
s = 2^(3*N);
i = 1;
    while i <= s
        if gcd(P(i,1),gcd(P(i,2),P(i,3))) == 1
            Q(end+1,:) = P(i,:);
  end
        i = i+1;
    end