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Fix Bh1-Bh2 swap bug in NRSur7dq4 when m1 < m2

Vijay Varma requested to merge waveforms/reviews/lalsuite:NRSur7dq4-review into master

Description

When m1 < m2, the NRSur7dq4 code previously did the following:

  1. Swap the labels of the two BH, i.e. m1 <-> m2, chi1 <-> chi2.
  2. Multiply the odd-m modes by -1 to undo this swap.

The assumption here is that the first step is only a rigid rotation by pi, and the second step undoes this rigid rotation.

However, the first step is only a rigid rotation if after the swap the in-plane spins are also rotated by pi. This is demonstrated here: https://git.ligo.org/waveforms/reviews/RemnantFits/wikis/home/label_swap_test

The previous code failed this test, as the in-plane spins were not rotated after the swap:
test_swap_before

This is now fixed:
test_swap

API Changes and Justification

Backwards Compatible Changes

  • This change introduces no API changes
  • This change adds new API calls

Backwards Incompatible Changes

  • This change modifies an existing API
  • This change removes an existing API

Review Status

This model is already reviewed: https://git.ligo.org/waveforms/reviews/nrsur7dq4/wikis/home This bug fix should not affect most PE runs as m1 < m2 is excluded in most cases anyway.

Edited by LALSuite Bot

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