Source code for

# Copyright (C) 2022 Andrew Williamson
# 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 3 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
# Public License for more details.
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# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

# =============================================================================
#                                   Preamble
# =============================================================================
""" This module contains functions for calculating and manipulating coherent

import numpy as np

[docs]def get_coinc_indexes(idx_dict, time_delay_idx): """Return the indexes corresponding to coincident triggers Parameters ---------- idx_dict: dict Dictionary of indexes of triggers above threshold in each detector time_delay_idx: dict Dictionary giving time delay index (time_delay*sample_rate) for each ifo Returns ------- coinc_idx: list List of indexes for triggers in geocent time that appear in multiple detectors """ coinc_list = np.array([], dtype=int) for ifo in idx_dict.keys(): # Create list of indexes above threshold in single detector in geocent # time. Can then search for triggers that appear in multiple detectors # later. if len(idx_dict[ifo]) != 0: coinc_list = np.hstack( [coinc_list, idx_dict[ifo] - time_delay_idx[ifo]] ) # Search through coinc_idx for repeated indexes. These must have been loud # in at least 2 detectors. counts = np.unique(coinc_list, return_counts=True) coinc_idx = counts[0][counts[1] > 1] return coinc_idx
[docs]def get_coinc_triggers(snrs, idx, t_delay_idx): """Returns the coincident triggers from the longer SNR timeseries Parameters ---------- snrs: dict Dictionary of single detector SNR time series idx: list List of geocentric time indexes of coincident triggers t_delay_idx: dict Dictionary of indexes corresponding to light travel time from geocenter for each detector Returns ------- coincs: dict Dictionary of coincident trigger SNRs in each detector """ coincs = {ifo: snrs[ifo][idx + t_delay_idx[ifo]] for ifo in snrs} return coincs
[docs]def coincident_snr(snr_dict, index, threshold, time_delay_idx): """Calculate the coincident SNR for all coincident triggers above threshold Parameters ---------- snr_dict: dict Dictionary of individual detector SNRs index: list List of indexes (geocentric) for which to calculate coincident SNR threshold: float Coincident SNR threshold. Triggers below this are cut time_delay_idx: dict Dictionary of time delay from geocenter in indexes for each detector Returns ------- rho_coinc: numpy.ndarray Coincident SNR values for surviving triggers index: list The subset of input indexes corresponding to triggers that survive the cuts coinc_triggers: dict Dictionary of individual detector SNRs for triggers that survive cuts """ # Restrict the snr timeseries to just the interesting points coinc_triggers = get_coinc_triggers(snr_dict, index, time_delay_idx) # Calculate the coincident snr snr_array = np.array( [coinc_triggers[ifo] for ifo in coinc_triggers.keys()] ) rho_coinc = abs(np.sqrt(np.sum(snr_array * snr_array.conj(), axis=0))) # Apply threshold thresh_indexes = rho_coinc > threshold index = index[thresh_indexes] coinc_triggers = get_coinc_triggers(snr_dict, index, time_delay_idx) rho_coinc = rho_coinc[thresh_indexes] return rho_coinc, index, coinc_triggers
[docs]def get_projection_matrix(f_plus, f_cross, sigma, projection="standard"): """Calculate the matrix that projects the signal onto the network. Definitions can be found in Fairhurst (2018) [arXiv:1712.04724]. For the standard projection see Eq. 8, and for left/right circular projections see Eq. 21, with further discussion in Appendix A. See also Williamson et al. (2014) [arXiv:1410.6042] for discussion in context of the GRB search with restricted binary inclination angles. Parameters ---------- f_plus: dict Dictionary containing the plus antenna response factors for each IFO f_cross: dict Dictionary containing the cross antenna response factors for each IFO sigma: dict Dictionary of the sensitivity weights for each IFO projection: optional, {string, 'standard'} The signal polarization to project. Choice of 'standard' (unrestricted; default), 'right' or 'left' (circular polarizations) Returns ------- projection_matrix: np.ndarray The matrix that projects the signal onto the detector network """ # Calculate the weighted antenna responses keys = sorted(sigma.keys()) w_p = np.array([sigma[ifo] * f_plus[ifo] for ifo in keys]) w_c = np.array([sigma[ifo] * f_cross[ifo] for ifo in keys]) # Get the projection matrix associated with the requested projection if projection == "standard": denom =, w_p) *, w_c) -, w_c) ** 2 projection_matrix = (, w_c) * np.outer(w_p, w_p) +, w_p) * np.outer(w_c, w_c) -, w_c) * (np.outer(w_p, w_c) + np.outer(w_c, w_p)) ) / denom elif projection == "left": projection_matrix = ( np.outer(w_p, w_p) + np.outer(w_c, w_c) + (np.outer(w_p, w_c) - np.outer(w_c, w_p)) * 1j ) / (, w_p) +, w_c)) elif projection == "right": projection_matrix = ( np.outer(w_p, w_p) + np.outer(w_c, w_c) + (np.outer(w_c, w_p) - np.outer(w_p, w_c)) * 1j ) / (, w_p) +, w_c)) else: raise ValueError( f'Unknown projection: {projection}. Allowed values are: ' '"standard", "left", and "right"') return projection_matrix
[docs]def coherent_snr( snr_triggers, index, threshold, projection_matrix, coinc_snr=None ): """Calculate the coherent SNR for a given set of triggers. See Eq. 2.26 of Harry & Fairhurst (2011) [arXiv:1012.4939]. Parameters ---------- snr_triggers: dict Dictionary of the normalised complex snr time series for each ifo index: numpy.ndarray Array of the indexes corresponding to triggers threshold: float Coherent SNR threshold. Triggers below this are cut projection_matrix: numpy.ndarray Matrix that projects the signal onto the network coinc_snr: Optional- The coincident snr for each trigger. Returns ------- rho_coh: numpy.ndarray Array of coherent SNR for the detector network index: numpy.ndarray Indexes that survive cuts snrv: dict Dictionary of individual deector triggers that survive cuts coinc_snr: list or None (default: None) The coincident SNR values for triggers surviving the coherent cut """ # Calculate rho_coh snr_array = np.array( [snr_triggers[ifo] for ifo in sorted(snr_triggers.keys())] ) snr_proj = np.inner(snr_array.conj().transpose(), projection_matrix) rho_coh2 = sum(snr_proj.transpose() * snr_array) rho_coh = abs(np.sqrt(rho_coh2)) # Apply thresholds above = rho_coh > threshold index = index[above] coinc_snr = [] if coinc_snr is None else coinc_snr if len(coinc_snr) != 0: coinc_snr = coinc_snr[above] snrv = { ifo: snr_triggers[ifo][above] for ifo in snr_triggers.keys() } rho_coh = rho_coh[above] return rho_coh, index, snrv, coinc_snr
[docs]def network_chisq(chisq, chisq_dof, snr_dict): """Calculate the network chi-squared statistic. This is the sum of SNR-weighted individual detector chi-squared values. See Eq. 5.4 of Dorrington (2019) []. Parameters ---------- chisq: dict Dictionary of individual detector chi-squared statistics chisq_dof: dict Dictionary of the number of degrees of freedom of the chi-squared statistic snr_dict: dict Dictionary of complex individual detector SNRs Returns ------- net_chisq: list Network chi-squared values """ ifos = sorted(snr_dict.keys()) chisq_per_dof = dict.fromkeys(ifos) for ifo in ifos: chisq_per_dof[ifo] = chisq[ifo] / chisq_dof[ifo] chisq_per_dof[ifo][chisq_per_dof[ifo] < 1] = 1 snr2 = { ifo: np.real(np.array(snr_dict[ifo]) * np.array(snr_dict[ifo]).conj()) for ifo in ifos } coinc_snr2 = sum(snr2.values()) snr2_ratio = {ifo: snr2[ifo] / coinc_snr2 for ifo in ifos} net_chisq = sum([chisq_per_dof[ifo] * snr2_ratio[ifo] for ifo in ifos]) return net_chisq
[docs]def null_snr( rho_coh, rho_coinc, apply_cut=True, null_min=5.25, null_grad=0.2, null_step=20.0, index=None, snrv=None ): """Calculate the null SNR and optionally apply threshold cut where null SNR > null_min where coherent SNR < null_step and null SNR > (null_grad * rho_coh + null_min) elsewhere. See Eq. 3.1 of Harry & Fairhurst (2011) [arXiv:1012.4939] or Eqs. 11 and 12 of Williamson et al. (2014) [arXiv:1410.6042].. Parameters ---------- rho_coh: numpy.ndarray Array of coherent snr triggers rho_coinc: numpy.ndarray Array of coincident snr triggers apply_cut: bool Apply a cut and downweight on null SNR determined by null_min, null_grad, null_step (default True) null_min: scalar Any trigger with null SNR below this is retained null_grad: scalar Gradient of null SNR cut where coherent SNR > null_step null_step: scalar The threshold in coherent SNR rho_coh above which the null SNR threshold increases as null_grad * rho_coh index: dict or None (optional; default None) Indexes of triggers. If given, will remove triggers that fail cuts snrv: dict of None (optional; default None) Individual detector SNRs. If given will remove triggers that fail cut Returns ------- null: numpy.ndarray Null SNR for surviving triggers rho_coh: numpy.ndarray Coherent SNR for surviving triggers rho_coinc: numpy.ndarray Coincident SNR for suviving triggers index: dict Indexes for surviving triggers snrv: dict Single detector SNRs for surviving triggers """ index = {} if index is None else index snrv = {} if snrv is None else snrv # Calculate null SNRs null2 = rho_coinc ** 2 - rho_coh ** 2 # Numerical errors may make this negative and break the sqrt, so set # negative values to 0. null2[null2 < 0] = 0 null = null2 ** 0.5 if apply_cut: # Make cut on null. keep = ( ((null < null_min) & (rho_coh <= null_step)) | ( (null < (rho_coh * null_grad + null_min)) & (rho_coh > null_step) ) ) index = index[keep] rho_coh = rho_coh[keep] snrv = {ifo: snrv[ifo][keep] for ifo in snrv} rho_coinc = rho_coinc[keep] null = null[keep] return null, rho_coh, rho_coinc, index, snrv
[docs]def reweight_snr_by_null( network_snr, null, coherent, null_min=5.25, null_grad=0.2, null_step=20.0): """Re-weight the detection statistic as a function of the null SNR. See Eq. 16 of Williamson et al. (2014) [arXiv:1410.6042]. Parameters ---------- network_snr: numpy.ndarray Array containing SNR statistic to be re-weighted null: numpy.ndarray Null SNR array coherent: Coherent SNR array Returns ------- rw_snr: dict Re-weighted SNR for each trigger """ downweight = ( ((null > null_min - 1) & (coherent <= null_step)) | ( (null > (coherent * null_grad + null_min - 1)) & (coherent > null_step) ) ) rw_fac = np.where( coherent > null_step, 1 + null - (null_min - 1) - (coherent - null_step) * null_grad, 1 + null - (null_min - 1) ) rw_snr = np.where(downweight, network_snr / rw_fac, network_snr) return rw_snr
[docs]def reweightedsnr_cut(rw_snr, rw_snr_threshold): """ Performs a cut on reweighted snr based on a given threshold Parameters ---------- rw_snr: array of reweighted snr rw_snr_threshhold: any reweighted snr below this threshold is set to 0 Returns ------- rw_snr: array of reweighted snr with cut values as 0 """ if rw_snr_threshold is not None: rw_snr = np.where(rw_snr < rw_snr_threshold, 0, rw_snr) return rw_snr