Problem with FFT Matlab code

Dear

I found a simple code for fft in below address

**broken link removed**

and converted in MATLAB code.(this is easy because matlab is as same as c code, but indeces start from 1 in matlab)

but my matlab function is not same as fft matlab fuction.

function X=DFT(x,N);
S=size(x);
X=[x,zeros(1,N-S(2))];
bit=log(N)/log(2);
N2=N/2;
k=0;
for n=0:N-2
if(n<k)
temp=X(k+1);
X(k+1)=X(n+1);
X(n+1)=temp;
end
m=N2;
while(m<=k)
k=k-m;
m=m/2;
end
k=k+m;
end
l2=1;
w=-1+0*i;
for loop=1:bit
l1=l2;
l2=l2*2;
u=1;
for n=0:l1-1
k=n;
while(k<N)
i1=k+l1+1;
temp=u*X(i1);
X(k+1)=X(k+1)+temp;
X(i1)=X(k+1)-temp;
k=k+l2;
end
u=u*w;
end
w=sqrt((1+real(w))/2)-sqrt((1-real(w))/2)*i;
end

Would you please help me to overcome this problem or send me a fft matlab code?

Best Rigards.

Re: Problem with fft

Why you want to write your own fft code in MATLAB ?:| There is a function fft () already existing.

Try these commands.

Demo .....(for a demo)
lookfor ........ ( say fft)
help..... (say fft)

i.e. type help fft

You will get it.

Re: Problem with fft

%FFT Discrete Fourier transform.
% FFT(X) is the discrete Fourier transform (DFT) of vector X. For
% matrices, the FFT operation is applied to each column. For N-D
% arrays, the FFT operation operates on the first non-singleton
% dimension.
%
% FFT(X,N) is the N-point FFT, padded with zeros if X has less
% than N points and truncated if it has more.
%
% FFT(X,[],DIM) or FFT(X,N,DIM) applies the FFT operation across the
% dimension DIM.
%
% For length N input vector x, the DFT is a length N vector X,
% with elements
% N
% X(k) = sum x*exp(-j*2*pi*(k-1)*(n-1)/N), 1 <= k <= N.
% n=1
% The inverse DFT (computed by IFFT) is given by
% N
% x = (1/N) sum X(k)*exp( j*2*pi*(k-1)*(n-1)/N), 1 <= n <= N.
% k=1
%
% See also FFT2, FFTN, FFTSHIFT, FFTW, IFFT, IFFT2, IFFTN.

% Copyright 1984-2005 The MathWorks, Inc.
% $Revision: 5.15.4.5 $ $Date: 2005/06/21 19:23:54 $

% Built-in function.

Re: Problem with fft

??? Input argument "x" is undefined.
this is the error ;
first input the sequence to it..

Re: Problem with fft

??? Input argument "x" is undefined.
this is the error ;
first input the sequence to it..

Click to expand...

you need to save the function in a file (called DFT.m), add it to your path, and then from the command window call it as DFT(x,N); where x is an array in your workspace and N is the length of the array.

Re: Problem with fft

n=input('enter the length of the dft sequence');
x=input('enter the sequence');
y=fft(x,n);
k=0:1:length;
stem(k,abs);
disp ('result is');
disp('y');
disp(abs);

it works!