Thanks Hong, this has been fixed by Stefano there: https://gitlab.com/petsc/petsc/-/commit/38faa66a3f98cdf432182095b5ca9cf1fc38724a?merge_request_iid=3717 <https://gitlab.com/petsc/petsc/-/commit/38faa66a3f98cdf432182095b5ca9cf1fc38724a?merge_request_iid=3717> Pierre
> On 17 Mar 2021, at 8:27 PM, Zhang, Hong <[email protected]> wrote: > > Pierre, > Do you mean a possible bug in C=AtB MatTransposeMatMult()? > Can you provide a stand-alone test without hpddm that reproduces this error? > Hong > From: petsc-dev <[email protected]> on behalf of Pierre Jolivet > <[email protected]> > Sent: Wednesday, March 17, 2021 4:31 AM > To: For users of the development version of PETSc <[email protected]> > Subject: [petsc-dev] MatTransposeMatMult() bug > > Hello, > While trying out Stefano’s PCApplyMat_MG() code (*), we stumbled upon weird > numerical errors when reusing a Mat for both MatProduct_AB and MatProduct_AtB. > This reminded me that there has been a long-standing issue with > MatTransposeMatMult(), see > https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/pc/impls/hpddm/hpddm.cxx.html#line608 > > <https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/pc/impls/hpddm/hpddm.cxx.html#line608>, > that I never looked into. > I’ve now been trying to figure this out, because this has side effects in > multiple places (PCMG and PCHPDDM at least), and thus could impact user-code > as well? > With this commit: > https://gitlab.com/petsc/petsc/-/commit/03d8bd538039defc2fcc3e37d523735c4aaceba0 > > <https://gitlab.com/petsc/petsc/-/commit/03d8bd538039defc2fcc3e37d523735c4aaceba0> > + > $ mpirun -n 4 src/ksp/ksp/tutorials/ex76 -ksp_converged_reason -pc_type hpddm > -pc_hpddm_levels_1_eps_nev 20 -ksp_type preonly -mat_type aij -load_dir > ${DATAFILESPATH}/matrices/hpddm/GENEO -rhs 2 -pc_hpddm_coarse_correction > balanced -C_input_mattransposematmult -D_output_mattransposematmult > I’m seeing that C is nonzero, but D is full of zeros. > Mat Object: 4 MPI processes > type: mpidense > 5.7098316584361917e-08 1.0159399260517841e-07 > 1.5812349976211856e-07 2.0688121715350138e-07 > 2.4887556933361981e-08 4.8111092300772958e-08 > 1.4606298643602107e-07 1.7213611729839211e-07 > […] > Mat Object: 4 MPI processes > type: mpidense > 0.0000000000000000e+00 0.0000000000000000e+00 > 0.0000000000000000e+00 0.0000000000000000e+00 > 0.0000000000000000e+00 0.0000000000000000e+00 > 0.0000000000000000e+00 0.0000000000000000e+00 > […] > > If one switches to a MatType which has no MatProduct_AtB implementation with > B of type MPIDense (reminder: in that case, the product is computed > column-by-column), e.g., -mat_type sbaij, one gets the expected result. > Mat Object: 4 MPI processes > type: mpidense > 7.2003197398135299e-01 9.5191869895699011e-01 > 6.1793966541680234e-02 9.3884397585488877e-01 > 1.0022337823233585e-02 2.4653068080134588e-01 > 1.4463931936094099e-01 8.6111517670701687e-01 > > Is there a bug somewhere with the MatAIJ implementation, or am I doing > something which is not allowed by the MatProduct() machinery? > > Thanks, > Pierre > > (*) https://gitlab.com/petsc/petsc/-/merge_requests/3717 > <https://gitlab.com/petsc/petsc/-/merge_requests/3717>
