# Hello everyone, I have a matlab problem and I don't know how to go about it.The question goes thus: Using a matlab code prove that for discrete time sinusoids whose frequencies are seperated by an integer multiple of 2*pi are identical. Pleas

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chafah zachary am 16 Jul. 2013
Hello everyone,
I have a matlab problem and I don't know how to go about it.The question goes thus:
Using a matlab code prove that for discrete time sinusoids whose frequencies are seperated by an integer multiple of 2*pi are identical.
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Youssef Khmou am 17 Jul. 2013
Bearbeitet: Youssef Khmou am 17 Jul. 2013
hi,
I think you mean that two sinusoidal functions whose phases are separated by integer multiple of 2*pi are identical :
Fs=40; % sample rate
f=15; % fundamental frequency
t=0:1/Fs:2-1/Fs;
b=2*pi*2; % phase multiple of 2*pi
y1=sin(2*pi*t*f);
y2=sin(2*pi*t*f+b);
figure, plot(t,y1,t,y2,'r')
rmse=sqrt(mean((y1-y2).^2));
norm(y1-y2);
now change b to another value, you will realize that they are not identical anymore .
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Muthu Annamalai am 16 Jul. 2013
Usually forum members don't provide canned homework solutions. You have a better chance to receive help when you show your work.
Having said, that you can learn solution to your problem by reading the help for FFT function at FFT Example section.
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Image Analyst am 16 Jul. 2013
What are identical? Surely sine waves of different frequencies are not identical. A sine wave of 314 hertz is not identical to one at 628 hertz or one at 942 Hertz. What is supposed to be identical here? They could be identical if you subsampled them at the proper subsampling rate.
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Matt J am 16 Jul. 2013
The OP mentions "discrete sinusoids". I think the idea is that
a(n) = sin(2*pi*f*n)
is identical to
b(n) = sin(2*pi*(f+m)*n)
for any integer m
Image Analyst am 17 Jul. 2013
And for only certain specific f and n, not for any and all values. A simple subtraction would work to show that they're equal at certain n indexes.

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