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fourier transform

Started by shareena_b April 13, 2008
hi all,

i have one function, x = (e^-2t) cos (4t) u(t) and i
suppose to compute this fourier transform for the
continuous signal and plot the frequency spectrum. these
are the step that i figure out that can verified my answer that i
calculated myself (correct me if im wrong)

1- plot the signal
2- use fft command
3- use fftshift command
4- use stem command

but, in the first step, i did this..

>> fo = 2/pi; %the frequency
>> Fs = 100; %the sampling rate
>> Ts = 1/Fs; %sampling time interval
>> t = 0 : Ts : 1-Ts; %sampling period
>> n = length (t); %number of samples
>> y = (exp(-2*t))*cos(4*t);
??? Error using ==> mtimes
Inner matrix dimensions must agree.

>>

i also tried this..

>> y = 3D(exp(-2*t)).*cos(4*t);
??? y = 3D(exp(-2*t)).*cos(4*t);
|
Error: Unexpected MATLAB operator.

and obviously the figure didnt come out. i tried other
command also but there are still errors.

how can i fix this? or are there any specific resources
that i can refer to? i already search at mathworks.com and this forum
and also some other signal and system books.

thank you.