Hey everyone, first of all id just like to clarify this isnt a homework or coursework related problem, its part of my personal MatLab learning for future years. I obtained a nice little siganls and systems question off a friend, it looked fairly simple but ive come across a problem which i cant find a solution to. Here goes...(adsbygoogle = window.adsbygoogle || []).push({});

Investigate the frequency content X(f) of a single 10 Hz sinewave, lasting for a time T_end. Set the sample frequency to be fs=1000, and T_end to be 2. Plot the absolute value of the function X(f) as a against frequency f.

Here is my code for this part.

function [x, t] = sinewave(T_end)

fs = 1000;

ts = 1/fs;

T = T_end;

t = 0:ts:T_end-ts;

f= -fs/2 : 1/T : fs/2-1/T; % sets the frequecncy axis, between -500 and (500-0.5).

x = sin(2.*pi.*f.*t);

X = fft(x);

Y = fftshift(X); % shifts right hand end to its alias below f=0, as graph is periodic this just centers the plot about 0.

stem(f,abs(Y),'k')

xlabel('frquency Hz');

ylabel('Abs(X)');

title('frequency content at T end = 2');

I believe this to be correct, and can explain the results obtained at different T_end values.

The next part of the question is where I get stuck.

Replace the line that defines x(t) with the code,

t1= 0:ts:1.0-ts;

x=0*t;

x(1:length(t1))=sin(2*pi*f*t1);

figure(1)

plot(t,x)

figure(2)

in order to create a pulse of length 1.

When this code is entered i get the standard, Error using ==> times

Matrix dimensions must agree.

Error in ==> sinwav at 9

x(1:length(t1))=sin(2*pi*f*t1);

I know this error occurs due to matrix multiplication, but simply .*'ing does not solve it,

the matrix sizes are apparaently as follows, x[1 x 2000] , t1[1 x 1000], t[1x2000],f[1 x 2000]. And im not actually sure if i should add the .'s and this would change the outcome.

Any comments or information would be greatly appericated, and hopefully this will help others as well.

Many Thanks

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# Matlab Matrix Multiplication Query in an fft application

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