Commits on Sep 4, 2024

1. Slightly relax tolerance in a test case of Apply1InteriorArbitrary …

   The test case in third_party/qsim/tests/mps_simulator_test.cc on
   line 262 fails if the Eigen linear algebra library is updated to a
   recent version available from https://gitlab.com/libeigen/eigen.
   Specifically, commit 59498c96 in the Eigen repo (which can be seen at
   https://gitlab.com/libeigen/eigen/-/merge_requests/1663) changed the
   code in Eigen/src/Core/arch/Complex.h for pmul() to use a fused
   multiply-add-subtract (FMA) instruction (fmaddsub) instead of the
   previous separate multiply and add-subtract instructions. The new code
   improved accuracy for many of the tests in mps_simulator_test.cc,
   slightly worsened accuracy for some of the tests, and in the case of
   the one on line 262, made it cross the absolute tolerance value of
   1e-5 by a very small amount. After considering various alternatives,
   the least-worst option seems to be to increase the tolerance for this
   one case.
   
   The qsim repository on GitHub has its own vendored copy of Eigen, so
   this change is not strictly necessary; however, if we ever update
   qsim's internal copy of Eigen, then this change will become relevant.
   
   Note: the original debugging & solution are the work of @pavoljuhas.

   

   mhucka committed Sep 4, 2024
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