Hi Stalin,
I assume you need to vectorize all the loops in your code. You could refer to a possible workaround here that reduces two of the loops in your code. It is difficult to reduce the third loop without re-writing the logic as index and pos variables change size iteration to iteration. Hope it helps.
function [ y ] = my_fft_for( x )
N1 = length(x); % calculates the size of the Xn sequence
nFFT = 2^ceil(log2(N1)); % calculates the number of samples to complete
x =[x zeros(1,nFFT-N1)]; % The sequence is completed with 0's to nFFT elements
N=length(x); % calculates the number of samples of xn
b=bin2dec(fliplr(dec2bin (0:1:nFFT-1)))+1; % Reordering of samples (reverse bit)
x=x(b); % Signal reordered
S=log2(N); % calculates the number of stages
Half=1;
for stage=1:S % FOR loop of stages of the algorithm Log2 (N)
index=0:(2^stage):(N-1); % Butterflies for each stage of the algorithm
n=0:(Half-1); % A butterfly is calculated and the result is saved
pos=n+index'+1; % Index of samples
pow=(2^(S-stage)).*n; % Power of complex multiplication
w=exp((-1i)*(2*pi).*pow/N); % Complex multiplication
a=x(pos)+x(pos+Half).*w; % First part of the butterfly
b=x(pos)-x(pos+Half).*w; % Second part of the butterfly
x(pos)=a; % Saving result of the first part of the butterfly
x(pos+Half)=b; % Saving result of the second part of the butterfly
Half=2*Half;
end % Calculating the next "Half" value
y=x;
% The result of the function is saved
end
