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<span style="color:rgb(32, 31, 30);font-family:"Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, system-ui, Roboto, "Helvetica Neue", sans-serif;font-size:15px;background-color:rgb(255, 255, 255);display:inline !important">Pierre,</span><br>
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<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<span style="color:rgb(32, 31, 30);font-family:"Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, system-ui, Roboto, "Helvetica Neue", sans-serif;font-size:15px;background-color:rgb(255, 255, 255);display:inline !important">Do you mean a
possible bug in C=<span style="background-color:rgb(255, 255, 255);display:inline !important">AtB <span style="background-color:rgb(255, 255, 255);display:inline !important">MatTransposeMatMult()?</span></span></span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<span style="color:rgb(32, 31, 30);font-family:"Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, system-ui, Roboto, "Helvetica Neue", sans-serif;font-size:15px;background-color:rgb(255, 255, 255);display:inline !important"><span style="background-color:rgb(255, 255, 255);display:inline !important"><span style="background-color:rgb(255, 255, 255);display:inline !important">Can
you provide a stand-alone test without hpddm that reproduces this error? </span></span></span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<span style="color:rgb(32, 31, 30);font-family:"Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, system-ui, Roboto, "Helvetica Neue", sans-serif;font-size:15px;background-color:rgb(255, 255, 255);display:inline !important"><span style="background-color:rgb(255, 255, 255);display:inline !important"><span style="background-color:rgb(255, 255, 255);display:inline !important">Hong</span></span></span></div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> petsc-dev <petsc-dev-bounces@mcs.anl.gov> on behalf of Pierre Jolivet <pierre@joliv.et><br>
<b>Sent:</b> Wednesday, March 17, 2021 4:31 AM<br>
<b>To:</b> For users of the development version of PETSc <petsc-dev@mcs.anl.gov><br>
<b>Subject:</b> [petsc-dev] MatTransposeMatMult() bug</font>
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<div class="" style="word-wrap:break-word; line-break:after-white-space">Hello,
<div class="">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.</div>
<div class="">This reminded me that there has been a long-standing issue with MatTransposeMatMult(), see <a href="https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/pc/impls/hpddm/hpddm.cxx.html#line608" class="">https://www.mcs.anl.gov/petsc/petsc-current/src/ksp/pc/impls/hpddm/hpddm.cxx.html#line608</a>,
that I never looked into.</div>
<div class="">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?</div>
<div class="">With this commit: <a href="https://gitlab.com/petsc/petsc/-/commit/03d8bd538039defc2fcc3e37d523735c4aaceba0" class="">https://gitlab.com/petsc/petsc/-/commit/03d8bd538039defc2fcc3e37d523735c4aaceba0</a></div>
<div class="">+</div>
<div class="">$ 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</div>
<div class="">I’m seeing that C is nonzero, but D is full of zeros.</div>
<div class="">
<div class="">Mat Object: 4 MPI processes</div>
<div class=""> type: mpidense</div>
<div class="">5.7098316584361917e-08 1.0159399260517841e-07</div>
<div class="">1.5812349976211856e-07 2.0688121715350138e-07</div>
<div class="">2.4887556933361981e-08 4.8111092300772958e-08</div>
<div class="">1.4606298643602107e-07 1.7213611729839211e-07</div>
</div>
<div class="">[…]</div>
<div class="">
<div class="">Mat Object: 4 MPI processes</div>
<div class=""> type: mpidense</div>
<div class="">0.0000000000000000e+00 0.0000000000000000e+00</div>
<div class="">0.0000000000000000e+00 0.0000000000000000e+00</div>
<div class="">0.0000000000000000e+00 0.0000000000000000e+00</div>
<div class="">0.0000000000000000e+00 0.0000000000000000e+00</div>
</div>
<div class="">[…]</div>
<div class=""><br class="">
</div>
<div class="">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.</div>
<div class="">
<div class="">Mat Object: 4 MPI processes</div>
<div class=""> type: mpidense</div>
<div class="">7.2003197398135299e-01 9.5191869895699011e-01</div>
<div class="">6.1793966541680234e-02 9.3884397585488877e-01</div>
<div class="">1.0022337823233585e-02 2.4653068080134588e-01</div>
<div class="">1.4463931936094099e-01 8.6111517670701687e-01</div>
</div>
<div class=""><br class="">
</div>
<div class="">Is there a bug somewhere with the MatAIJ implementation, or am I doing something which is not allowed by the MatProduct() machinery?</div>
<div class=""><br class="">
</div>
<div class="">Thanks,</div>
<div class="">Pierre</div>
<div class=""><br class="">
</div>
<div class="">(*) <a href="https://gitlab.com/petsc/petsc/-/merge_requests/3717" class="">https://gitlab.com/petsc/petsc/-/merge_requests/3717</a> </div>
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