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Function: qn_filter()

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, $q(t)$, is the function

\begin{displaymath}
q(t) = e^{-\pi ft/Q}\cos(2\pi ft)
\end{displaymath} (8.10.183)

where $f$ is the central frequency and $Q$ 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 up previous contents
Next: Function: qn_normalize() Up: GRASP Routines: Black hole Previous: Function: qn_qring()   Contents
Bruce Allen 2000-11-19