How to form a matrix

I am using 'for loop' with variable 'i' to run something. i.e. for i = 1:100, .... Say, I want to record the value of i when it equals to 4, 6, 9, 12. How can I group them into a matrix so that the output can be like, M = [4 6 9 12]?

Answer 1

[David Young]

The question doesn't entirely make sense. You say you want to record the value of i when i equals 4, 6, 9, 12. Taking the question literally, you could do this

k = 0;                         % initialise index into M
for i = 1:100
  if ismember(i, [4 6 9 12])   % test whether i is at an interesting place
    k = k + 1;                 % increment index
    M(k) = i;                  % store the value of i in M
  end
end

but if that was really what you wanted you'd just do

M = [4 6 9 12];

in the first place.

Perhaps you could clarify what exactly you need to do.

(By the way, some people regard i as a bad choice of name for a variable, because it is also a name for the square root of -1 in MATLAB.)

[Patrick]

Sorry for not being clear but you got what I mean, thanks for your help, David.