Reply by September 15, 20072007-09-15
Hi, All
I have original mass spectrom which is time domain signal. Then I use fft
in Matlab to fourier transform into powerspectrum. Code as below:

%load data into a single column matrix called "a"
At(a,65536); %built in m file, fft of matrix a for 2^16 element.
Pa=A.*conj(A)/65536; %calculate the intensity of A
f = (0:32768)/65536; % create the frequency of x-axis
h=ones(1,32769); %create a vector of 1
g=h./f; %the frequency of x-axis
m=g/16;%factor the number of sample points.


Now I have question on how to perform inverse FFT for just part of the
result of FFT in the region of (200:5000)? And how to calculate the x
Thanks for advance.