MATLAB: For loop not working when run inside a function!

for loopfunctionindex exceeds matrix dimensions

I have a for loop inside a function Function. When I call that function within a script I get an error Index exceeds matrix dimensions and it points to a specific line of Function. This line of code that is pointed out corresponds to a for loop.
The for loop is built for following case:
I have two matrices of size.
 B (400x30)
 C (1x30)
From these matrices I need to get a matrix A (400×30) that is obtained in the way
A(1,1) = B(1,1)*C(:,1)...A(  1,30) = B(  1,30)*C(:,30)
A(2,1) = B(2,1)*C(:,1)...A(400,30) = B(400,30)*C(:,30)
The for loop I wrote in order to get A is following:
for  p = 1:400;
    for i = 1:30;
        A(p,i) = C(p,i)*B(:,i);
    end
end
Calling the function Function within a script I get the error, but if I go inside the function and evaluate the lines of code line by line, I don't get any error for the for loop, I can calculate the A matrix easily.
I really don't understand why is this happening, and I need to call Function within a script? But with getting this error constantly I can not move further with the code.
Many thanks,

Best Answer

This sounds like magic:
 Calling the function Function within a script I get the error,
 but if I go inside the function and evaluate the lines of code
 line by line, I don't get any error for the for loop.
Matlab does not do any magic. It is not getting clear to me, when the problem occurres, but you can be sure that there is a deterministic resaon for this. You can use the debugger to see, what happens. Type this in the command window:
dbstop if error
Now run the code again. If Matlab stops at the error, check the sizes of the used variables in the failing line:
% A(p,i) = C(p,i)*B(:,i);  % Assumed offending line
p
i
size(C)
size(B)
But perhaps the error appears anywhere else. This would be clear, if you post the complete error message, not just a part of it.
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