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Example: compare_chirps program

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This example compares a chirp generated by sp_filters() to a chirp with identical parameters generated by make_filters(); the output is shown in Figure [*]. The chirp generated by sp_filters() is transformed to the time domain, and the two chirps are superimposed on one graph. Includes/compare_chirps.tex Note that to get the graph to show both chirps as simultaneous functions of time, sp_filters() needed to know the coalescence time found by make_filters(), so the latter function is called first. If the coalescence time input to sp_filters() had been zero , its chirp would have finished at the beginning--or equivalently, the end--of the time-domain data.

Also note that the inverse realft() of the stationary phase chirp had to be multiplied by a factor to be comparable to the time-domain chirp. The 2/LENGTH factor is left out of the inverse realft(), and the SRATE factor is needed to keep the dimensions right. (Also, the forward realft() of the time-domain chirp would need to be multiplied by 1/SRATE to compare to the stationary phase chirp.)

Figure: The output of compare_chirps, comparing the stationary-phase approximate waveform FFT'd into the time domain (red curve) with a 2nd-order post-Newtonian chirp calculated in the time domain, using make_filters() (black curve). The lower part of the graph shows three interesting regions of the upper (complete) graph. The bottom left detail shows the Gibbs startup-transient, the bottom middle detail shows a typical region of good agreement, and the bottom right detail shows the Gibbs turn-off transient. The Gibbs startup transient is also visible at the far right of the upper figure, which is periodically identified with the far left.


next up previous contents
Next: Wiener (optimal) filtering Up: GRASP Routines: Gravitational Radiation Previous: Function: sp_filters()   Contents
Bruce Allen 2000-11-19