How do I perform fft in MATLAB without inbuilt function?

Why wouldn't you want to use the inbuilt function?

Otherwise - write your own.

• Define a function called fft
• Google/work out how an fft is performed (here seems a good start)
• Transcribe that algorithm into your function
• Call your new function

I'm not entirely sure what benefit that gives you over the inbuilt method, but there you go.

This is a function which performs a discrete Fourier transform (greatest accuracy is achieved with the highest N)

function X = dft(x,N)
   %fast Fourier transform
   
   X = zeros(1,length(X));
   
   k=1;
    
   while k<length(X);
       n=0;
       tempSum=0;
       while n<N
           tempSum = tempSum + x(n)*exp(-1i * 2*pi*k*n/N);
           n=n+1;
       X(k) =tempSum; 
       k=k+1;

To make it a fast Fourier transform, you need to work out which bits you can shave off, or what bits you can reuse.

I leave that as an exercise to the reader….

(But here's a hint….someone has already gone through all of that bother for you….it's called the inbuilt method)

For any help- MATLABSolutions