Error- using --- .* -- Matrix dimensions must agree.

Hello everyone I am new to Matlab and have a simple question. The error I am receiving is one that I don't fully understand. I have tried changing the .* to a * in my equation but still come up with the same error. I am sure it is something that I am completely overlooking and cant figure it out any help would be appreciated. My error is in x = Xk .* cos((fk * pi) .* t);

function [x,t] = syn_sin(fk,Xk,fs,dur, tstart)
%SYN-SIn   FUnction to sythesize a sum of cosine waves
%   Usage:
% [xx,tt] = syn_sin(fk,Xk,fs,dur,tstart)
%       fk = vector of frequencies
%               (these could be negative or positive)
%       Xk = vector of complex amplitudes: Amp*e*exp(j*phase)
%       fs = the number of samples per second for the time axis
%       dur = total time duration of the signal
%       tstart = starting time(default is zero, if you make this input
%       optional)
%       xx = vector of sinusoidal values
%       tt = vector of times, for the time axis
%
%
%       note: fk and XK must be the same length.
%               Xk(1) = corresponds to frequency in fk(1),
%               Xk(2) = corresponds to frequency in fk(2), etc

t = (tstart:1/(fs):dur);

x = Xk .* cos((fk * pi) .* t);

size(Xk)
size(fk)

plot (x,t);
shg

the size of Xk = 1 3
the size of fk = 1 3

I figured I would check the dimensions.

[Erik S.]

what is the size of t?

[Guillaume]

Next time, select your code and click on the {} Code button to format it properly, like I've done for you this time.

Answer 1

[Guillaume]

If xk and fk have the same size, then obviously, it's the third vector t that is a different size.

I don't see how you guarantee that t is the same length as Xk and fk. Moreover, your t calculation looks wrong, you're going from a point in time tstart to a duration dur. Maybe you meant:

t = tstart:1/fs:tstart + dur;

This still does not guarantee that t has the same number of elements as xk.

[Jonathan Herron]

thanks for the help.

Answer 2

[Stephen23]

This should solve the different size issue:

t = linspace(tstart, tstart+dur, numel(Xk));

[Jonathan Herron]

Thanks for the help. I will try this out.