# Building a matrix using while loops? (MATLAB)

• MATLAB
Building a matrix using "while" loops? (MATLAB)

Hello

Here is my code:

Code:
i = 1;
j = 1;
S = zeros(11,11);

while i < 12
while j < 12
S(i,j) = Test1(a(i,j),b(i,j),c(i,j));
j = j + 1;
end
i = i + 1;
end

a,b,c are all 11x11 matrices and Test1 is a function m-file which outputs a number. (I have tested it for all the values that a(i,j), b(i,j) and c(i,j) take).

My code is only calculating the first row of S, ie. S(2,1) = 0 still. I don't know why the program is ending without adding 1 onto i and repeating the loop, I can only imagine the "while" loop is the wrong way of going about this?

Thanks for any help,

Mike

## Answers and Replies

Mark44
Mentor

A better choice is a for loop for each of your loops.
Code:
for i=1:11
for j = 1:11
%% loop body
end
end

You can do what you're doing with while loops, but they are in a sense more primitive control structures, so you have to do more of the work in your code. I think what might be happening is that after the inner loop has gone through a complete set of iterations, and i is now 2, you still have the last value of j (=12) in your inner loop. A fix for this problem might be like so:
Code:
while i < 12
j = 1   %% added this line
while j < 12
S(i,j) = Test1(a(i,j),b(i,j),c(i,j));
j = j + 1;
end
i = i + 1;
end