On 14/10/15 20:40, Ian Hinder wrote:
The second problem is that when I switch to OpenBLAS in the test parameter files, all tests pass except for CTThorns/CT_MultiLevel/test/boostedpuncture.par, which fails with
ml_bssn-ml_ham.d.asc: substantial differences significant differences on 56 (out of 109) lines maximum absolute difference in column 13 is 16.796401082424 maximum relative difference in column 13 is 10.214243488001 (insignificant differences on 45 lines) ml_bssn-ml_ham.x.asc: substantial differences significant differences on 88 (out of 182) lines maximum absolute difference in column 13 is 5.30707663071086 maximum relative difference in column 13 is 0.897391183181081 (insignificant differences on 94 lines) ml_bssn-ml_ham.y.asc: substantial differences significant differences on 88 (out of 182) lines maximum absolute difference in column 13 is 5.30900732375572 maximum relative difference in column 13 is 0.897408813491657 (insignificant differences on 94 lines) ml_bssn-ml_ham.z.asc: substantial differences significant differences on 56 (out of 109) lines maximum absolute difference in column 13 is 5.30900949367607 maximum relative difference in column 13 is 0.8974032303582 (insignificant differences on 53 lines)
All other solution variables are within tolerance, suggesting that the solver is getting the right answer, though ml_ham would be more sensitive to small solution differences anyway. None of the other CT_MultiLevel tests seem to be checking ml_ham, so it might be that if ml_ham was checked, it would also differ. Could this be related to the McLachlan rewrite, or is the Hamiltonian constraint expected to be the same across the rewrite? It could be the usual roundoff-error problem, but the differences listed are quite large. Or maybe this comes from the method used by the elliptic solver, which may not be 100% deterministic due to thread ordering in the Gauss Seidel method?
Hi Ian,
thanks for detecting this. As this is meant as a general-purpose solver, not all the tests involve McLachlan (or even General Relativity). So you are right: what you see may be a generic problem with the computation of the Hamiltonian constraint, and not something specific to the puncture test.
The test, however, passes (at least on my workstation) using BLAS/LAPACK, so the McLachlan rewrite does not necessarily have to be responsible for the differences you see. Do you know if there are other tests that compute ml_ham and are affected by a swap between the two library implementations?
As for the first point you raise, I have just pushed a change following Roland's suggestion to remove the redundant "ActiveThorns" line from the test parfiles.
Best, Eloisa