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Hana,</div>
<div class="elementToProof"><span style="font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, "system-ui", Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);"><i>"product
AB with A nest, B nest"</i></span><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"> is not supported by PETSc. I do not know why PETSc does not display such an
error message. I'll check it.</span></div>
<div class="elementToProof"><span style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">Hong</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-users <petsc-users-bounces@mcs.anl.gov> on behalf of Hana Honnerová <hhornik@kma.zcu.cz><br>
<b>Sent:</b> Thursday, February 8, 2024 4:45 AM<br>
<b>To:</b> petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov><br>
<b>Subject:</b> [petsc-users] question on PCLSC with matrix blocks of type MATNEST</font>
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<p>Hi all,</p>
<p>I am trying to solve linear systems arising from isogeometric discretization (similar to FEM) of the Navier-Stokes equations in parallel using PETSc. The linear systems are of saddle-point type, so I would like to use the PCFIELDSPLIT preconditioner with
the -pc_fieldsplit_detect_saddle_point option, Schur complement factorization and the LSC Schur complement preconditioner. I do not provide any user-defined operators for PCLSC in my codes (at least for now).
</p>
<p>I store the matrix as a MATNEST consisting of 4 blocks (F for velocity-velocity part, Bt for velocity-pressure part, B for pressure-velocity part and NULL for pressure-pressure part). It is also convenient for me to store the blocks F, Bt and B as another
MATNEST consisting of blocks corresponding to individual velocity components. <br>
</p>
<p><br>
However, in this setting, I get the following error message:<br>
</p>
<p><i>[0]PETSC ERROR: Petsc has generated inconsistent data<br>
[0]PETSC ERROR: Unspecified symbolic phase for product AB with A nest, B nest. Call MatProductSetFromOptions() first<br>
[0]PETSC ERROR: See <a class="x_moz-txt-link-freetext" href="https://petsc.org/release/faq/">
https://petsc.org/release/faq/</a> for trouble shooting.<br>
[0]PETSC ERROR: Petsc Release Version 3.20.4, unknown <br>
[0]PETSC ERROR: /home/hhornik/gismo/build-petsc-mpi/RelWithDebInfo/bin/gsINSSolverPETScTest on a arch-debug named ThinkPad-T14 by hhornik Thu Feb 8 11:04:17 2024<br>
[0]PETSC ERROR: Configure options PETSC_ARCH=arch-debug --with-debugging=1 --download-mumps --download-scalapack<br>
[0]PETSC ERROR: #1 MatProductSymbolic() at /home/hhornik/Software/PETSc/src/mat/interface/matproduct.c:807<br>
[0]PETSC ERROR: #2 MatProduct_Private() at /home/hhornik/Software/PETSc/src/mat/interface/matrix.c:10027<br>
[0]PETSC ERROR: #3 MatMatMult() at /home/hhornik/Software/PETSc/src/mat/interface/matrix.c:10103<br>
[0]PETSC ERROR: #4 PCSetUp_LSC() at /home/hhornik/Software/PETSc/src/ksp/pc/impls/lsc/lsc.c:79<br>
[0]PETSC ERROR: #5 PCSetUp() at /home/hhornik/Software/PETSc/src/ksp/pc/interface/precon.c:1080<br>
[0]PETSC ERROR: #6 KSPSetUp() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:415<br>
[0]PETSC ERROR: #7 KSPSolve_Private() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:832<br>
[0]PETSC ERROR: #8 KSPSolve() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:1079<br>
[0]PETSC ERROR: #9 PCApply_FieldSplit_Schur() at /home/hhornik/Software/PETSc/src/ksp/pc/impls/fieldsplit/fieldsplit.c:1165<br>
[0]PETSC ERROR: #10 PCApply() at /home/hhornik/Software/PETSc/src/ksp/pc/interface/precon.c:498<br>
[0]PETSC ERROR: #11 KSP_PCApply() at /home/hhornik/Software/PETSc/include/petsc/private/kspimpl.h:383<br>
[0]PETSC ERROR: #12 KSPFGMRESCycle() at /home/hhornik/Software/PETSc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c:123<br>
[0]PETSC ERROR: #13 KSPSolve_FGMRES() at /home/hhornik/Software/PETSc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c:235<br>
[0]PETSC ERROR: #14 KSPSolve_Private() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:906<br>
[0]PETSC ERROR: #15 KSPSolve() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:1079<br>
[0]PETSC ERROR: #16 applySolver() at /home/hhornik/gismo/optional/gsIncompressibleFlow/src/gsINSSolver.hpp:531</i></p>
<p><i><br>
</i>I could not find any solution for this so far. My question is: Is it possible to use the LSC preconditioner in such case, where the matrix blocks are of type MATNEST? And if so, how?</p>
<p>Thank you,<br>
Hana Honnerova<br>
</p>
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