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int qn_filter(float freq, float qual,
float dt, float atten, int max, float **filterPtr)
Quasinormal ringdown waveforms are characterized by two parameters:
the central frequency of the waveform, and the quality of the
waveform. The parameter space is most easily described in terms of
these variables (rather than the mass and the angular momentum of the
corresponding black hole), so it is useful to construct filters for
quasinormal ringdown waveform searches in terms of the frequency and
quality of the waveform. This routine constructs such a filter, with
a specified frequency and quality. The routine returns
the number of filter elements computed before a specified attenuation
level was reached. The arguments are:
 freq: Input. The central frequency, in Hertz, of the
ringdown filter.
 qual: Input. The quality of the ringdown filter.
 dt: Input. The time interval, in seconds, between successive
data points in the returned waveform.
 atten: Input: The attenuation level, in dB, at which the
routine will terminate calculation of the waveforms.
 max: Input. The maximum number of data points to be returned
in the waveforms.
 filterPtr: Input/Output. A pointer to an array which, on
return, contains the filter sampled at intervals
dt. If the array has the value NULL on input, the routine
allocates an amount of memory to *filterPtr to hold max
elements.
The constructed filter, , is the function

(8.10.183) 
where is the central frequency and is the quality. The routine
qn_filter() performs no normalization, nor does it account for
different possible starting phases. The latter is not important for
detection template construction. Normalization is achieved using the
function qn_normalize(), which is described later.
 Author: Jolien Creighton, jolien@tapir.caltech.edu
Next: Function: qn_normalize()
Up: GRASP Routines: Black hole
Previous: Function: qn_qring()
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Bruce Allen
20001119