Clear Filters
Clear Filters

Why do I need to declare a variable inside a nested 'for' loop?

1 view (last 30 days)
Hi, I have some code, below, which fails on the last line before both 'end's (T_noise_out(it) = ....). The Command Window tells me that this is due to T_noise_out being an unrecognised variable. However, just a few lines above it, I am able to use 'F_noise_in(term_num)' and 'F_noise_out(term_num)' without explicitly declaring them. Why is this? I anticipated that this code would create an array of complex numbers called T_noise_out.
%term loop
for term_num = 1: 2: nterms
fprintf('Processing term %g of %g \n', term_num, nterms);
%Add new Fourier coefficient
F_noise_in(term_num) = -i*4/(pi*term_num);
F_noise_out(term_num) = F_noise_in(term_num).*H(term_num);
for it = 1: 1: ntsamples
t = (it-1).*dt;
real_F_noise_out = real(F_noise_out(term_num));
imag_F_noise_out = imag(F_noise_out(term_num));
T_noise_out(it) = T_noise_out(it)+real_F_noise_out*cos(2*pi*f0*term_num*t)-imag_F_noise_out*sin(2*pi*f0*term_num*t);

Accepted Answer

Adam on 22 Oct 2019
Edited: Adam on 22 Oct 2019
You are referring to it on the right-hand side of the equation as well as on the left. First time round it does not exist yet so that will error. You would need to initialise it before your outer loop to contain 0s of the correct size if you intend to store a running sum in it.
  1 Comment
Ted Baker
Ted Baker on 22 Oct 2019
Thanks Adam for the clear answer. For reference, my working code is as follows:
T_noise_out = zeros(1,ntsamples,'uint32');
for term_num = 1: 2: nterms
fprintf('Processing term %g of %g \n', term_num, nterms);
%etc etc etc...

Sign in to comment.

More Answers (0)


Find more on Loops and Conditional Statements in Help Center and File Exchange


Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!