please how to write this in matlab?

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Abdelrazzak rifai
Abdelrazzak rifai 2018-4-16
评论： Abdelrazzak rifai 2018-4-16
fourier function
  • define a sum of cosine waves f=8 HZ
  • build it's plot in time domain
  • build the plot of it's magnitude spectrumi don't understand how to use the arry in matlab :( :(

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回答（2 个）

Ngoc Thanh Hung Bui
I dont really understand the problem, better more specifically
KALYAN ACHARJYA
KALYAN ACHARJYA 2018-4-16
编辑：KALYAN ACHARJYA 2018-4-16 
 % Are you looking for this one 
t=0:1:115;
fs=500 % Assumed Sampling Frequency
f=8; % Given 8 Hz
cw=cos(2*pi*f/fs*t);
subplot(121);stem(cw,'r'); title('Time Domain');
%Read in Signal Processing Book How to find Magnitute Response
fftLength=512;
sigLength=length(cw);
win=rectwin(sigLength)'; % Window Selection 'Ractangular'
y=fft(cw.*win,fftLength);
length=fftLength/2+1;
% Magnitude Response 
subplot(122);plot([1:length]*fs/(2*length),abs(y(1:length)));
title('Magnitude Response');
  2 个评论
Abdelrazzak rifai
Abdelrazzak rifai 2018-4-16
the professor gave us :
#s=fft(U);
build plot of complex spectrum
1:M=√a^2+b^2
2:MS=abs(S)
3: plot(ms)
4:he gave us:complex exponential and Fourier function and he told us using vector and bla bla bla..
Abdelrazzak rifai
Abdelrazzak rifai 2018-4-16
x(t)=A*cos(2*pi*frequency*time+pi/6)
  • pi/6=30 phase shift of the cosine in degree
  • A=1,frequency=8,phase=pi/6; or 30 degree,time=0:1:115;(but how can i understand these step?please..so how can i build the magnitude spectrum?i want to understand please..

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