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Calculating velocity correlation function

  1. May 28, 2012 #1

    I have been trying to write a code to calculate velocity correlation function so that I can obtain a frequency spectrum for my system on taking a fourier transform. For testing my code I generated a sine wave data and calculated vcf and took dft. I got correct frequency value but the peak splits into two (the value should be 1.6 but I get two peaks 1.58 and 1.62) and there are several small peaks in the spectrum.

    I am pasting the vcf calculation part below. Could someone please help me find a flaw in my logic?

    Thanks a lot!

    vcf = 0
    do m = 2, Nmax, dnsample !loop thorugh all time origins
    do n = 2, Nmax-m, dnsample !loop over velocity at time t points
    vdot = vm * v(m+n)
    vmag = v(m+n) * v(m+n)
    vcf = vcf + (vdot/vmag)
    end do
    time = m*0.5*1d-13
    vcf = vcf*norm
    write(4,*) time, vcf
    end do
  2. jcsd
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