how to find fft

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shilpa s 2016-4-18

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https://ww2.mathworks.cn/matlabcentral/answers/279613-how-to-find-fft

编辑： Walter Roberson 2016-4-20

hai frnds,

i have 7653 values for bond length of OH bond in water during spectral analysis.so now the next step is to find the fft of the bond length.value of time varies as (0:.725:5548.425).please generate the code for me.I am stucked

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Behind The Sciences 2016-4-18

Have a look to this post to understand what you want to do: http://www.behindthesciences.com/signal-processing/fouriertransformtheory

Then,have a look to this post to get code that you need: http://www.behindthesciences.com/signal-processing/fouriertransformmatlabtutorial

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Star Strider 2016-4-18

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See this documentation for the fft function. The code between the top two plot figures has everything you need to analyse and plot your Fourier transformed data.

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Star Strider 2016-4-19

The frequencies sort themselves.

To find the peaks and the associated frequencies, use the findpeaks function on the absolute value of the fft, just as you plotted them here.

shilpa s 2016-4-20

编辑：Walter Roberson 2016-4-20

在 MATLAB Online 中打开

my code is as follows

   T=0.075*10^-15;
   Fs=1/T;
   x=fblAvgs+sblAvgs %first bond length averages+second bond length                   %averages
     L=length(x);
     Y=fft(x);
  w=Y.*conj(Y)/L;
  f=Fs/L*w(0:L/2);
  plot(f,w(1:L/2+1))
  xlabel(frequency)
  ylabel(magnitude)