XPipeline Review Meeting Monday 28 July 2008 09:00 Pacific / 12:00 Eastern
Agenda: Monday 28 July 2008 09:00 Pacific / 12:00 Eastern

Updates on reviewers' analyses of GRBs.
 Instructions and suggested GRB assignments: [ text ].

Code walkthrough: m2html documentation for revision 2301 [ web ]
 We are currently at line 712 of xdetection.m.
Minutes:
Attendance: Patrick, Gareth, Xavi
 Starting at xdetection line 712: Right before data conditioning and ffts
 723730 Create cell arrays to contain results for different analysisTimes. Cell arrays are arrays that can hold miscellaneous data types, very flexible
 739936 loop over analysisTimes
 755 If using real data: Use Linear Predictor Error Filter (LPEF) to condition data in xcondition, can train filter using analysis data (line 756) or can load precomputed filter (line 765). Only difference between xcondition calls is final arg which determines LPEF coeffiecients. In production analysis we train LPEF using analysis data, i.e., line 756
 xdetection reviewed to line 777, moving to look at xcondition.
 Patrick: Commenting and doc needs improving (ticket created)
 Xavi: Worried that filter is not long enough
 Patrick: Take 256s of time domain data, FFT it, square it to obtain something like PSD, IFFT it and take first second of this autocorrelation function to train filter using inbuilt matlab functions
 Xavi: suggesting increasing whitening time upwards from 1s, he uses 4s in matched filter
 Patrick: Ideas for tests of this code (see end of minutes)
 Patrick: Also noticed some overwhitening (i.e., notching) of spectral lines, not worried about this since overwhitening is preferred to underwhitening. Xavi agrees
 Patrick: explains input args to xcondition.m training mode is set to 'search' for production runs
 xcondition lines 100112: hard coded params
 Xavi: are these filters FIR?
 Patrick: No, filtering takes place in freq domain
 xcondition lines 114235: check input args
 xcondition line 188191: analysisTime is length of FFT which will be applied to data, check that whitening time is longer than this analysisTime so that on this scale the data appears white
 xcondition line 218: In production analysis we always set training mode to 'search' Other options used in coherent follow up searches where we want to train filters while avoiding a short stretch of data containing event candidate of interest
 xcondition lines 255265: Resample data using standard matlab function resample.m
 Xavi: concerned that ignoring only data near NYQUIST frequency might not be sufficient to avoid effects of aliasing
 Finished review of xcondition at line 277
 Tests to be performed:
 i) Post some plots of conditioned data using different whitening times, compare Gaussianity.
 ii) Check that conditioned data is found to be white by independent method
 iii) Check that output statistics follow chisquares
 iv) Plot autocorrelation function for different whitening times
 v) Investigate effects of aliasing at frequencies below NYQUIST (see comments ~line 255)
$Id: minutes20080728.html,v 1.3 2008/07/28 17:21:26 gareth Exp $