how to repeat cycles in a DFT equation

Question

steven 2013-7-28

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Hello, I have to write a code for a DFT equation. I have the code for 1 cycle below and it comes out fine. Now I have to repeat the cycle 100 times with the same x(n). I am trying to repeat with a for loop but can't get the summation right.

n=0:1:1/f; %sequence of time samples

X=cos(2*pi*f*n); %first part of equation

Xz= [(X) zeros(1,10)]; %padding zeros

Xs=0;

so I end up saying I want to repeat Xz 100 cycles

for t=0:100 Xs(t+1)=Xs(t+1)+Xz end

but matlab says the sides are not equal? Any help would be great.

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Answer 1

Azzi Abdelmalek 2013-7-28

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https://ww2.mathworks.cn/matlabcentral/answers/83408-how-to-repeat-cycles-in-a-dft-equation#answer_92969

编辑：Azzi Abdelmalek 2013-7-28

在 MATLAB Online 中打开

Use repmat function

repmat(Xz,100,1)

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steven 2013-7-28

在 MATLAB Online 中打开

Thanks, ok I see the matlab has made 100 copies, but it won't graph correctly now.

Xs=repmat(Xz,100,1);

Xw=zeros(1,N);%put zeros in Xw

for k=0:N-1 %loop for k

    for n=0:N-1  % loop for n
        Xw(k+1)=Xw(k+1)+Xs(n+1)*exp((-j*2*pi*n*k)/N); %DFT equation
    end
end

When I do my for loops with the one cylce the graph comes out correctly, but when I replace it with the Xs that holds my 100 cycles the graph comes out wrong? Shouldn't the DFT algorithm do it through all the cycles now?

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