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##

Function: `avg_inv_spec()`

0
`void avg_inv_spec(float flo,float srate,int n,double decay,double *norm,
float *htilde, float* mean_pow_spec,float* twice_inv_noise)`

This function maintains an auto-regressive moving average (see `avg_spec()`) of the power spectrum , and an array containing
, which can be used for optimal filtering. This latter array
is set to zero below a specified cuff-off frequency .
The arguments are:

`flo:` Input. The low frequency cut-off , in Hz.
`srate:` Input. The sample rate, in Hz.
`n:` Input. The number of points in the arrays.
`decay:` Input. The quantity as defined in `avg_spec()`.
Sets the characteristic decay time for the auto-regressive average.
`norm:` Input/Ouput. Used for internal storage. Set to when you want to begin
a new auto-regressive average. Must not be altered otherwise.
`htilde:` Input. The array `htilde[0..n-1]` contains the positive frequency FFT of
the metric perturbation.
`mean_pow_spec:` Output. The array `mean_pow_spec[0..n/2]` contains the
mean power spectrum. Should be zeroed when resetting to begin a new average. The array
element `mean_pow_spec[0]` contains the power spectrum at DC, and the array
element `mean_pow_spec[n/2]` contains the power spectrum at the Nyquist frequency
`srate`/2.
`twice_inv_noise:` Output. The array ` twice_inv_noise[0..n/2]` contains . It is set to zero for
. The array element `twice_inv_noise[0]` contains
the DC value, and the array element `twice_inv_noise[n/2]`
contains the value at the Nyquist frequency `srate`/2.

- Author:
Bruce Allen, ballen@dirac.phys.uwm.edu
- Comments:
We assume here that the ``correct" thing to do is the average the
spectrum, then invert it. There may be a better way to construct
the weight function for an optimal filter, however.

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** Up:** GRASP Routines: Gravitational Radiation
** Previous:** Function: correlate()
** Contents**
Bruce Allen
2000-11-19