what is the difference in fft(x,1024) and fft(x,2048)?

x=fft(x,1024);
x=fft(x,2048);
x=fft(x);

%what is the difference between all these if i have done zero padding and the length of the signal is 2048 .

Answer 1

[Matt J]

The 2nd and 3rd cases are equivalent. The 1st case is the same as if you had discarded the last 1024 x(i), as can be seen from,

x=rand(1,2048);

isequal(  fft(x,1024)  ,fft(x(1:1024)) )

ans = logical
   1