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      Compute an ensemble averaged cross spectrum of real data.


Calling Sequence

      sxy = xspec(x,y,n,sr,[freq])


      x = input signal number 1. in
      y = input signal number 2. in
        If x or y have too few points, -1 is returned.
      n = number of points to use in each transform in
        May be arbitrary.
      sr = sample rate in Hz (Def=1 Hz) in
        Needed to get actual units.

Keyword Parameters


        OVERLAP=novr number of points to overlap spectra.
        TRANSFER_FUNCT = transfer function, Txy = Sxy/Sxx
          in units of y/x
        CA_ARRAY = ca : Coherence and autospectra array.
          ca(*,0)=Cxy(f) Coherence=|Sxy|^2/(Sxx*Syy) dimensnless
          ca(*,1) = Sxx(f) Autospectrum of x in units of x**2/Hz.
          ca(*,2) = Syy(f) Autospectrum of y in units of y**2/Hz.
        N_ENSEMBLE=n returned # spectra ensemble averaged.
        /NOTES lists some additional comments.


      sxy = spectral density in units of x*y/Hz. out
        First value is DC, last is Nyquist.
      freq = optionally output frequency array. out

Common Blocks



      Notes: Restricted to one dimensional data only.


Modification History

      B. L. Gotwols Mar. 1, 1993
      R. E. Sterner Mar. 1, 1993 --- cleaned up some.
      BLG, RES --- Mar. 10, 1993 --- renamed variables.
      BLG --- 19 May, 1993 --- made loop index long.
      Fixed ntimes to be correct. Also floated sr.
      Made OVERLAP default to 0 to be consistent with
      future addition of OVERLAP in rspec and cspec.
  Copyright (C) 1993, Johns Hopkins University/Applied Physics Laboratory
  This software may be used, copied, or redistributed as long as it is not
  sold and this copyright notice is reproduced on each copy made. This
  routine is provided as is without any express or implied warranties
  whatsoever. Other limitations apply as described in the file disclaimer.txt.

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