Module LALSimNoise.c

Detailed Description

Routines to produce a continuous stream of simulated gravitational-wave detector noise.

Prototypes
int	XLALSimNoise (REAL8TimeSeries *s, size_t stride, REAL8FrequencySeries *psd, gsl_rng *rng)
	Routine that may be used to generate sequential segments of data with a specified stride from one segment to the next. More...

Function Documentation

XLALSimNoise()

int XLALSimNoise	(	REAL8TimeSeries *	s,
		size_t	stride,
		REAL8FrequencySeries *	psd,
		gsl_rng *	rng
	)

Routine that may be used to generate sequential segments of data with a specified stride from one segment to the next.

Calling instructions: for the first call, set stride = 0; subsequent calls should pass the same time series and have non-zero stride. This routine will advance the time series by an amount given by the stride and will generate new data so that the data is continuous from one segment to the next. For example: the following routine will output a continuous stream of detector noise with an Initial LIGO spectrum above 40 Hz:

#include <stdio.h>
#include <gsl/gsl_rng.h>
#include <lal/LALStdlib.h>
#include <lal/FrequencySeries.h>
#include <lal/TimeSeries.h>
#include <lal/Units.h>
#include <lal/LALSimNoise.h>
void mkligodata(void)
{
        const double flow = 40.0; // 40 Hz low frequency cutoff
        const double duration = 16.0; // 16 second segments
        const double srate = 16384.0; // sampling rate in Hertz
        size_t length = duration * srate; // segment length
        size_t stride = length / 2; // stride between segments
        LIGOTimeGPS epoch = { 0, 0 };
        REAL8FrequencySeries *psd;
        REAL8TimeSeries *seg;
     gsl_rng *rng;
        gsl_rng_env_setup();
        rng = gsl_rng_alloc(gsl_rng_default);
        seg = XLALCreateREAL8TimeSeries("STRAIN", &epoch, 0.0, 1.0/srate, &lalStrainUnit, length);
     psd = XLALCreateREAL8FrequencySeries("LIGO SRD", &epoch, 0.0, 1.0/duration, &lalSecondUnit, length/2 + 1);
     XLALSimNoisePSD(psd, flow, XLALSimNoisePSDiLIGOSRD);
        XLALSimNoise(seg, 0, psd, rng); // first time to initialize
     while (1) { // infinite loop
                double t0 = XLALGPSGetREAL8(&seg->epoch);
                size_t j;
        for (j = 0; j < stride; ++j) // output first stride points
                        printf("%.9f\t%e\n", t0 + j*seg->deltaT, seg->data->data[j]);
        XLALSimNoise(seg, stride, psd, rng); // make more data
        }
}

If only one single segment of data is required, set stride to be the length of the timeseries data vector. This will make a single segment of data that is not periodic (also, in this case it will not advance the epoch of the timeseries).

Note

• If stride = 0, initialize h by generating one (periodic) realization of noise; subsequent calls should have non-zero stride.
• If stride = h->data->length then generate one segment of non-periodic noise by generating two different realizations and feathering them together.

Warning

Only the first stride points are valid.

Parameters

	s	[in/out] noise time series
[in]	stride	stride (samples)
[in]	psd	power spectrum frequency series
[in]	rng	GSL random number generator

Definition at line 144 of file LALSimNoise.c.