simulateCW.py

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# Copyright (C) 2017 Karl Wette
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2 of the License, or (at your
# option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
# Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
## \defgroup lalpulsar_py_simulateCW SimulateCW
## \ingroup lalpulsar_python
r"""
Generate strain time series of a continuous-wave signal in the detector frame,
given a function which computes signal phase and amplitudes as functions of time.
 
The given function should compute quantities \f$\Delta\phi(t)\f$, \f$a_+(t)\f$,
and \f$a_\times(t)\f$ such that the plus and cross gravitational-wave
polarisations \f$h_+(t)\f$ and \f$h_\times(t)\f$ are given by:
\f{eqnarray}{
h_+(t)      & = & a_+(t)     \cos[\phi_0 + \Delta\phi(t)] \; , \\
h_\times(t) & = & a_\times(t)\sin[\phi_0 + \Delta\phi(t)] \; .
\f}
 
This module provides a class CWSimulator() to generate the strain time series.
CWSimulator() can also directly write frame files and SFT files. Example usage:
 
~~~
import lal
from lalpulsar import simulateCW
 
def waveform(h0, cosi, freq, f1dot):
    def wf(dt):
        dphi = lal.TWOPI * (freq * dt + f1dot * 0.5 * dt**2)
        ap = h0 * (1.0 + cosi**2) / 2.0
        ax = h0 * cosi
        return dphi, ap, ax
    return wf
 
tref     = 900043200
tstart   = 900000000
Tdata    = 86400
h0       = 1e-24
cosi     = 0.123
psi      = 2.345
phi0     = 3.210
freq     = 10.0
f1dot    = -1.35e-8
dt_wf    = 5
alpha    = 6.12
delta    = 1.02
detector = 'H1'
 
wf = waveform(h0, cosi, freq, f1dot)
S = simulateCW.CWSimulator(tref, tstart, Tdata, wf, dt_wf, phi0, psi, alpha, delta, detector)
 
# To write SFT files
for file, i, N in S.write_sft_files(fmax=32, Tsft=1800, comment="simCW"):
    print('Generated SFT file %s (%i of %i)' % (file, i+1, N))
 
# To write frame files
for file, i, N in S.write_frame_files(fs=1, Tframe=1800, comment="simCW"):
    print('Generated frame file %s (%i of %i)' % (file, i+1, N))
 
~~~
"""
## @{
 
from __future__ import division, print_function
 
import os
import sys
import re
import math
 
import lal
import lalpulsar
 
from . import git_version
 
__author__ = "Karl Wette <karl.wette@ligo.org>"
__version__ = git_version.id
__date__ = git_version.date
 
 
class CWSimulator(object):
    def __init__(
        self,
        tref,
        tstart,
        Tdata,
        waveform,
        dt_wf,
        phi0,
        psi,
        alpha,
        delta,
        det_name,
        earth_ephem_file="earth00-40-DE405.dat.gz",
        sun_ephem_file="sun00-40-DE405.dat.gz",
        tref_at_det=False,
        extra_comment=None,
    ):
        """
        Initialise a continuous-wave signal simulator.
 
        @param tref: reference time of signal phase at Solar System barycentre, in GPS seconds
            (but see @b tref_at_det)
        @param tstart: start time of signal, in GPS seconds
        @param Tdata: total duration of signal, in seconds
        @param waveform: function which computes signal phase and amplitudes as functions of time:
            @b dphi, @b aplus, @b across = @b waveform(dt), where:
                @b dt = time since reference time @b tref;
                @b dphi = phase of signal at time @b dt relative to reference time @b tref, in radians;
                @b aplus = strain amplitude of plus polarisation at time @b dt;
                @b across = strain amplitude of cross polarisation at time @b dt
        @param dt_wf: sampling time of the function @c waveform; this need only be small enough to ensure
            that @c dphi, @c aplus, and @c across are smoothly interpolated, and does not need to make
            the desired sampling frequency of the output strain time series
        @param phi0: initial phase of the gravitational-wave signal at @b tstart, in radians
        @param psi: polarisation angle of the gravitational-wave source, in radians
        @param alpha: right ascension of the gravitational-wave source, in radians
        @param delta: declination  of the gravitational-wave source, in radians
        @param det_name: name of the gravitational-wave detector to simulate a response for;
            e.g. @c "H1" for LIGO Hanford, @c "L1" for LIGO Livingston, @c "V1" for Virgo
        @param earth_ephem_file: name of file to load Earth ephemeris from
        @param sun_ephem_file: name of file to load Sun ephemeris from
        @param tref_at_det: default False; if True, shift reference time @b tref so that @b dt = 0 is
            @b tref in @e detector frame instead of Solar System barycentre frame, useful if e.g. one
            wants to turn on signal only for @b dt > 0, one can use @b tref as the turn-on time
        @param extra_comment: additional text to add to comment string in frame/SFT headers
               (not filenames), e.g. for wrapper script commandlines
        """
 
        self.__origin_str__origin_str = "Generated by %s, %s-%s (%s)" % (
            __file__,
            git_version.id,
            git_version.status,
            git_version.date,
        )
        if extra_comment:
            self.__origin_str__origin_str += ", " + extra_comment
 
        # store arguments
        self.__tstart__tstart = tstart
        self.__Tdata__Tdata = Tdata
 
        # parse detector name
        try:
            _, self.__site_index__site_index = lalpulsar.FindCWDetector(det_name, True)
            assert self.__site_index__site_index >= 0
        except:
            raise ValueError("Invalid detector name det_name='%s'" % det_name)
        self.__site__site = lal.CachedDetectors[self.__site_index__site_index]
 
        # load Earth and Sun ephemerides
        self.__ephemerides__ephemerides = lalpulsar.InitBarycenter(earth_ephem_file, sun_ephem_file)
 
        if tref_at_det:
            # calculate barycentric delay at reference time
            bary_state = lalpulsar.EarthState()
            bary_input = lalpulsar.BarycenterInput()
            bary_emit = lalpulsar.EmissionTime()
            bary_input.tgps = tref
            bary_input.site = self.__site__site
            for i in range(0, 3):
                bary_input.site.location[i] /= lal.C_SI
            bary_input.alpha = alpha
            bary_input.delta = delta
            bary_input.dInv = 0.0
            lalpulsar.BarycenterEarth(bary_state, bary_input.tgps, self.__ephemerides__ephemerides)
            lalpulsar.Barycenter(bary_emit, bary_input, bary_state)
 
            # adjust reference time so that dt = 0 is tref in detector frame
            tref += bary_emit.deltaT
 
        # start signal time series 'Tpad_wf' before/after output strain time series
        # add sufficient padding to signal for maximum Doppler modulation time shifts, otherwise
        # lalpulsar.PulsarSimulateCoherentGW() will output zeros without complaint (unless
        # you run with LAL_DEBUG_LEVEL=warning)
        Tpad_wf = 2.0 * lal.AU_SI / lal.C_SI
        tstart_wf = tstart - Tpad_wf
        Nwf = int(math.ceil(float(Tdata + 2 * Tpad_wf) / float(dt_wf)))
 
        # create REAL8TimeSeries to store signal phase
        self.__phi__phi = lal.CreateREAL8TimeSeries(
            "phi", tstart_wf, 0, dt_wf, lal.DimensionlessUnit, Nwf
        )
 
        # create REAL4TimeVectorSeries to store signal amplitudes
        # - LAL provides no creator function for this type, so must be done manually
        self.__a__a = lal.REAL4TimeVectorSeries()
        self.__a__a.name = "a+,ax"
        self.__a__a.epoch = tstart_wf
        self.__a__a.deltaT = dt_wf
        self.__a__a.f0 = 0
        self.__a__a.sampleUnits = lal.StrainUnit
        self.__a__a.data = lal.CreateREAL4VectorSequence(Nwf, 2)
 
        # call waveform() to fill time series of signal phase and amplitudes
        dt = float(tstart_wf - tref)
        for i in range(0, Nwf):
            dphi, aplus, across = waveform(dt)
            self.__phi__phi.data.data[i] = phi0 + dphi
            self.__a__a.data.data[i][0] = aplus
            self.__a__a.data.data[i][1] = across
            dt += dt_wf
 
        # create and initialise PulsarCoherentGW struct
        self.__wf__wf = lalpulsar.PulsarCoherentGW()
        self.__wf__wf.position.system = lal.COORDINATESYSTEM_EQUATORIAL
        self.__wf__wf.position.longitude = alpha
        self.__wf__wf.position.latitude = delta
        self.__wf__wf.psi = psi
        self.__wf__wf.phi = self.__phi__phi
        self.__wf__wf.a = self.__a__a
 
        # create and initialise PulsarDetectorResponse struct
        self.__detector__detector = lalpulsar.PulsarDetectorResponse()
        self.__detector__detector.site = self.__site__site
        self.__detector__detector.ephemerides = self.__ephemerides__ephemerides
 
    def _simulate_coherent_gw(self, h, noise_sqrt_Sh, noise_seed):
        # generate strain time series
        lalpulsar.PulsarSimulateCoherentGW(h, self.__wf__wf, self.__detector__detector)
 
        # add Gaussian noise, if requested
        if noise_sqrt_Sh > 0:
            assert noise_seed is not None
            assert noise_seed > 0
            noise_sigma = math.sqrt(0.5 / h.deltaT) * noise_sqrt_Sh
            lalpulsar.AddGaussianNoise(h, noise_sigma, noise_seed)
 
    def get_strain(self, fs, tmin=0, tmax=None, noise_sqrt_Sh=0, noise_seed=None):
        """
        Generate strain time series of a continuous-wave signal in the detector frame.
 
        @param fs: sampling frequency of strain time series, in Hz
        @param tmin: start time for strain time series, as offsets from self.__tstart
        @param tmax: start time for strain time series, as offsets from self.__tstart
        @param noise_sqrt_Sh: if >0, add Gaussian noise with square-root single-sided power
            spectral density given by this value, in Hz^(-1/2)
        @param noise_seed: use this seed for the random number generator used to create noise;
            required if noise_sqrt_Sh >0
 
        @return (@b t, @b h), where:
            @b t = start of time strain time series, in GPS seconds;
            @b h = strain time series
        """
 
        # process tmin/tmax range (interpreted relative to self.__tstart)
        if (tmin < 0) or (tmin >= self.__Tdata__Tdata):
            raise ValueError("tmin must be within [0,{}).".format(self.__Tdata__Tdata))
        if tmax is None:
            tmax = self.__Tdata__Tdata
        elif (tmax <= 0) or (tmax > self.__Tdata__Tdata):
            raise ValueError("tmax must be within (0,{}].".format(self.__Tdata__Tdata))
        tspan = tmax - tmin
 
        # create REAL4TimeSeries to store output time series
        Nh = int(fs * tspan)
        h = lal.CreateREAL4TimeSeries(
            "h", self.__tstart__tstart + tmin, 0, 1.0 / fs, lal.DimensionlessUnit, Nh
        )
 
        # generate strain time series
        self._simulate_coherent_gw_simulate_coherent_gw(h, noise_sqrt_Sh, noise_seed)
        return (h.epoch, h.data.data)
 
    def get_strain_blocks(self, fs, Tblock, noise_sqrt_Sh=0, noise_seed=None):
        """
        Generate strain time series of a continuous-wave signal in the detector frame, in contiguous blocks.
 
        @param fs: sampling frequency of strain time series, in Hz
        @param Tblock: length of each block, in seconds; should divide evenly into @b Tdata
        @param noise_sqrt_Sh: if >0, add Gaussian noise with square-root single-sided power
            spectral density given by this value, in Hz^(-1/2)
        @param noise_seed: use this seed for the random number generator used to create noise;
            if None, generate a random seed using os.urandom()
 
        @return (@b t, @b h, @b i, @b N), where:
            @b t = start of time strain time series, in GPS seconds;
            @b h = strain time series;
            @b i = block index, starting from zero;
            @b N = number of blocks
 
        This is a Python generator function and so should be called as follows:
        ~~~
        S = CWSimulator(...)
        for t, h, i, N in S.get_strain_blocks(...):
            ...
        ~~~
        """
 
        # work out number of blocks
        Nblock = int(round(self.__Tdata__Tdata / Tblock))
        if Tblock * Nblock > self.__Tdata__Tdata:
            raise ValueError(
                "Length of block Tblock=%g does not divide evenly into Tdata=%g"
                % (Tblock, self.__Tdata__Tdata)
            )
 
        # if no noise seed is given, generate a (non-zero) random seed using os.urandom()
        if not noise_seed:
            noise_seed = 0
            while not (0 < noise_seed and noise_seed < lal.LAL_INT4_MAX - Nblock):
                noise_seed = int.from_bytes(os.urandom(4), sys.byteorder, signed=False)
 
        # generate strain time series in blocks of length 'Tblock'
        tmin = 0
        for iblock in range(0, Nblock):
            epoch, hoft = self.get_strainget_strain(
                fs,
                tmin=tmin,
                tmax=tmin + Tblock,
                noise_sqrt_Sh=noise_sqrt_Sh,
                noise_seed=noise_seed + iblock,
            )
            yield epoch, hoft, iblock, Nblock
            tmin += Tblock
 
    def write_frame_files(
        self, fs, Tframe, comment="simCW", out_dir=".", noise_sqrt_Sh=0, noise_seed=None
    ):
        """
        Write frame files [1] containing strain time series of a continuous-wave signal.
 
        The strain time series is written as double-precision post-processed data (ProcData) channel named
        <tt>&lt;detector&gt;:SIMCW-STRAIN</tt>,
        where <tt>&lt;detector&gt;</tt> is the 2-character detector prefix (e.g. <tt>H1</tt> for LIGO Hanford,
        <tt>L1</tt> for LIGO Livingston, <tt>V1</tt> for Virgo).
 
        @param fs: sampling frequency of strain time series, in Hz
        @param Tframe: length of each frame, in seconds; should divide evenly into @b Tdata
        @param comment: frame file name comment, may only contain A-Z, a-z, 0-9, _, +, # characters
        @param out_dir: output directory to write frame files into
        @param noise_sqrt_Sh: if >0, add Gaussian noise with square-root single-sided power
            spectral density given by this value, in Hz^(-1/2)
        @param noise_seed: use this seed for the random number generator used to create noise;
            if None, generate a random seed using os.urandom()
 
        @return (@b file, @b i, @b N), where:
            @b file = name of frame file just written;
            @b i = frame file index, starting from zero;
            @b N = number of frame files
 
        This is a Python generator function and so should be called as follows:
        ~~~
        S = CWSimulator(...)
        for file, i, N in S.write_frame_files(...):
            ...
        ~~~
 
        [1] https://dcc.ligo.org/LIGO-T970130/public
        """
 
        try:
            import lalframe
        except ImportError:
            raise ImportError("SWIG wrappings of LALFrame cannot be imported")
 
        # check for valid frame filename comment (see LIGO-T010150)
        valid_comment = re.compile(r"^[A-Za-z0-9_+#]+$")
        if not valid_comment.match(comment):
            raise ValueError(
                "Frame file comment='%s' may only contain A-Z, a-z, 0-9, _, +, # characters"
                % comment
            )
 
        # generate strain time series in blocks of length 'Tframe'
        frame_h = None
        for t, h, i, N in self.get_strain_blocksget_strain_blocks(
            fs, Tframe, noise_sqrt_Sh=noise_sqrt_Sh, noise_seed=noise_seed
        ):
            # create and initialise REAL8TimeSeries to write to frame files
            if frame_h is None:
                frame_h_channel = "%s:SIMCW-STRAIN" % self.__site__site.frDetector.prefix
                frame_h = lal.CreateREAL8TimeSeries(
                    frame_h_channel, t, 0, 1.0 / fs, lal.DimensionlessUnit, len(h)
                )
            frame_h.epoch = t
            frame_h.data.data = h
 
            # create standard frame file name (see LIGO-T010150)
            frame_src = self.__site__site.frDetector.prefix[0]
            frame_desc = comment
            frame_t0 = int(t.gpsSeconds)
            frame_Tdata = int(math.ceil(float(t + Tframe)) - math.floor(float(t)))
            frame_name = "%s-%s-%u-%u.gwf" % (
                frame_src,
                frame_desc,
                frame_t0,
                frame_Tdata,
            )
            frame_path = os.path.join(out_dir, frame_name)
 
            # create frame
            frame_det_bits = 2 * self.__site_index__site_index
            frame = lalframe.FrameNew(
                t, Tframe, self.__class__.__name__, -1, i, frame_det_bits
            )
 
            # add strain time series to frame
            lalframe.FrameAddREAL8TimeSeriesProcData(frame, frame_h)
 
            # add history
            lalframe.FrameAddFrHistory(frame, "origin", self.__origin_str__origin_str)
 
            # write frame
            lalframe.FrameWrite(frame, frame_path)
 
            # yield current file name for e.g. printing progress
            yield frame_path, i, N
 
    def get_sfts(
        self,
        fmax,
        Tsft,
        noise_sqrt_Sh=0,
        noise_seed=None,
        window="rectangular",
        window_param=0,
    ):
        """
        Generate SFTs [2] containing strain time series of a continuous-wave signal.
 
        @param fmax: maximum SFT frequency, in Hz
        @param Tsft: length of each SFT, in seconds; should divide evenly into @b Tdata
        @param noise_sqrt_Sh: if >0, add Gaussian noise with square-root single-sided power
            spectral density given by this value, in Hz^(-1/2)
        @param noise_seed: use this seed for the random number generator used to create noise;
            if None, generate a random seed using os.urandom()
        @param window: if not None, window the time series before performing the FFT, using
            the named window function; see XLALCreateNamedREAL8Window()
        @param window_param: parameter for the window function given by @b window, if needed
 
        @return (@b sft, @b i, @b N), where:
            @b sft = SFT;
            @b i = SFT file index, starting from zero;
            @b N = number of SFTs
 
        This is a Python generator function and so should be called as follows:
        ~~~
        S = CWSimulator(...)
        for sft, i, N in S.get_sfts(...):
            ...
        ~~~
 
        [2] https://dcc.ligo.org/LIGO-T040164/public
        """
 
        # create timestamps for generating one SFT per time series
        sft_ts = lalpulsar.CreateTimestampVector(1)
        sft_ts.deltaT = Tsft
 
        # generate strain time series in blocks of length 'Tsft'
        sft_h = None
        sft_fs = 2 * fmax
        for t, h, i, N in self.get_strain_blocksget_strain_blocks(
            sft_fs, Tsft, noise_sqrt_Sh=noise_sqrt_Sh, noise_seed=noise_seed
        ):
            # create and initialise REAL8TimeSeries to write to SFT files
            if sft_h is None:
                sft_name = self.__site__site.frDetector.prefix
                sft_h = lal.CreateREAL8TimeSeries(
                    sft_name, t, 0, 1.0 / sft_fs, lal.DimensionlessUnit, len(h)
                )
            sft_h.epoch = t
            sft_h.data.data = h
 
            # create SFT, possibly with windowing
            sft_ts.data[0] = t
            sft_vect = lalpulsar.MakeSFTsFromREAL8TimeSeries(
                sft_h, sft_ts, window, window_param
            )
 
            # yield current SFT
            yield sft_vect.data[0], i, N
 
    def write_sft_files(
        self,
        fmax,
        Tsft,
        comment="simCW",
        out_dir=".",
        noise_sqrt_Sh=0,
        noise_seed=None,
        window="rectangular",
        window_param=0,
    ):
        """
        Write SFT files [2] containing strain time series of a continuous-wave signal.
 
        @param fmax: maximum SFT frequency, in Hz
        @param Tsft: length of each SFT, in seconds; should divide evenly into @b Tdata
        @param comment: SFT file name comment, may only contain A-Z, a-z, 0-9 characters
        @param out_dir: output directory to write SFT files into
        @param noise_sqrt_Sh: if >0, add Gaussian noise with square-root single-sided power
            spectral density given by this value, in Hz^(-1/2)
        @param noise_seed: use this seed for the random number generator used to create noise;
            if None, generate a random seed using os.urandom()
        @param window: if not None, window the time series before performing the FFT, using
            the named window function; see XLALCreateNamedREAL8Window()
        @param window_param: parameter for the window function given by @b window, if needed
 
        @return (@b file, @b i, @b N), where:
            @b file = name of SFT file just written;
            @b i = SFT file index, starting from zero;
            @b N = number of SFT files
 
        This is a Python generator function and so should be called as follows:
        ~~~
        S = CWSimulator(...)
        for file, i, N in S.write_sft_files(...):
            ...
        ~~~
 
        [2] https://dcc.ligo.org/LIGO-T040164/public
        """
 
        # check for valid SFT filename comment (see LIGO-T040164)
        valid_comment = re.compile(r"^[A-Za-z0-9]+$")
        if not valid_comment.match(comment):
            raise ValueError(
                "SFT file comment='%s' may only contain A-Z, a-z, 0-9 characters"
                % comment
            )
 
        # create SFT filename specification
        spec = lalpulsar.SFTFilenameSpec()
        spec.path = out_dir
        spec.window_type = window
        spec.window_param = window_param
        spec.privMisc = comment
 
        # generate SFTs
        for sft, i, N in self.get_sftsget_sfts(
            fmax,
            Tsft,
            noise_sqrt_Sh=noise_sqrt_Sh,
            noise_seed=noise_seed,
            window=window,
            window_param=window_param,
        ):
            # write SFT
            lalpulsar.WriteSFT2StandardFile(sft, spec, self.__origin_str__origin_str)
 
            # yield current file name for e.g. printing progress
            sft_path = lalpulsar.BuildSFTFilenameFromSpec(spec)
            yield sft_path, i, N
 
 
## @}