On Dec 10, 2024, at 11:20 AM, Matteo Semplice <matteo.semplice@uninsubria.it> wrote:
Thanks, Barry.

Just to be sure, one should refer to the help of https://petsc.org/release/manualpages/DM/DMCreateInterpolationScale/ and the vec should be set to the point-wise inverse of (INTERPOLATION)*(vector of ones) ?

Matteo

On 10/12/2024 16:38, Barry Smith wrote:

It appears you are completely ignoring the vec argument? Take a look at, for example, DMCreateInterpolation_DA() you will see you need to provide an appropriate vec in the same way you need (and do) provide an appropriate mat.

Barry

On Dec 10, 2024, at 7:02 AM, Matteo Semplice via petsc-users <petsc-users@mcs.anl.gov> wrote:

Dear petsc-users,

    I am trying with a student to modify the MG example 65 to use mat-shells instead of assembled matrices. Our use case is for a method that will use custom shell operators and shell interpolation/restrictions.

To start we have modified ex65 and tried to replace the standard restriction/interpolation with a shell matrix that performs the same operations on the DMDA grids.

I attach our modifications to ex65.

The problem is that the code sometimes completes execution and sometimes errors out like

$ ./ex65shell -ksp_monitor -pc_type mg -da_refine 2 -ksp_rtol 1e-1
>> Created DMshell 0x55bbc83c91a0 (0x55bbc8390a80)
Calling KSPSolve from main
computeRHS on grid 513
computeMatrix on grid 513
Inside Coarsen
>> Created DMshell 0x55bbc84c5270 (0x55bbc84b2ff0)
Inside Coarsen
>> Created DMshell 0x55bbc84e0a30 (0x55bbc84bdb60)
>> Create interpolation from 0x55bbc84c5270(0x55bbc84b2ff0) to 0x55bbc83c91a0(0x55bbc8390a80)
[0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
[0]PETSC ERROR: Invalid pointer
[0]PETSC ERROR: Invalid Pointer to PetscObject: Argument 'obj' (parameter # 1)
[0]PETSC ERROR: See https://petsc.org/release/faq/ for trouble shooting.
[0]PETSC ERROR: Petsc Release Version 3.22.0, unknown
[0]PETSC ERROR: ./ex65shell with 1 MPI process(es) and PETSC_ARCH on signalkuppe by matteo Tue Dec 10 12:55:12 2024
[0]PETSC ERROR: Configure options: --prefix=/home/matteo/software/petscsaved/3.22-opt/ PETSC_DIR=/home/matteo/software/petsc --PETSC_ARCH=dbg --with-debugging=1 --with-st
rict-petscerrorcode --download-hdf5 --download-ml --with-metis --with-parmetis --with-gmsh --with-triangle --with-zlib --with-p4est-dir=~/software/p4est/local/
[0]PETSC ERROR: #1 PetscObjectReference() at /home/matteo/software/petsc/src/sys/objects/inherit.c:620
[0]PETSC ERROR: #2 PCMGSetRScale() at /home/matteo/software/petsc/src/ksp/pc/impls/mg/mgfunc.c:394
[0]PETSC ERROR: #3 PCSetUp_MG() at /home/matteo/software/petsc/src/ksp/pc/impls/mg/mg.c:998
[0]PETSC ERROR: #4 PCSetUp() at /home/matteo/software/petsc/src/ksp/pc/interface/precon.c:1071
[0]PETSC ERROR: #5 KSPSetUp() at /home/matteo/software/petsc/src/ksp/ksp/interface/itfunc.c:415
[0]PETSC ERROR: #6 KSPSolve_Private() at /home/matteo/software/petsc/src/ksp/ksp/interface/itfunc.c:826
[0]PETSC ERROR: #7 KSPSolve() at /home/matteo/software/petsc/src/ksp/ksp/interface/itfunc.c:1075
[0]PETSC ERROR: #8 main() at ../src/ex65shell.c:79
[0]PETSC ERROR: PETSc Option Table entries:
[0]PETSC ERROR: -da_refine 2 (source: command line)
[0]PETSC ERROR: -ksp_monitor (source: command line)
[0]PETSC ERROR: -ksp_rtol 1e-1 (source: command line)
[0]PETSC ERROR: -pc_type mg (source: command line)
[0]PETSC ERROR: ----------------End of Error Message -------send entire error message to petsc-maint@mcs.anl.gov----------

In all cases valgrind complains like

$ valgrind ./ex65shell -ksp_monitor -pc_type mg -da_refine 2 -ksp_rtol 1e-1 -int_view ascii::ascii_info
==2130767== Memcheck, a memory error detector
==2130767== Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward et al.
==2130767== Using Valgrind-3.19.0 and LibVEX; rerun with -h for copyright info
==2130767== Command: ./ex65shell -ksp_monitor -pc_type mg -da_refine 2 -ksp_rtol 1e-1 -int_view ascii::ascii_info
==2130767==
hwloc x86 backend cannot work under Valgrind, disabling.
May be reenabled by dumping CPUIDs with hwloc-gather-cpuid
and reloading them under Valgrind with HWLOC_CPUID_PATH.
>> Created DMshell 0xfbf50f0 (0xfb49480)
Calling KSPSolve from main
computeRHS on grid 513
computeMatrix on grid 513
Inside Coarsen
>> Created DMshell 0xff404a0 (0xff062d0)
Inside Coarsen
>> Created DMshell 0xff78ca0 (0xff4a530)
>> Create interpolation from 0xff404a0(0xff062d0) to 0xfbf50f0(0xfb49480)
Mat Object: 1 MPI process
type: shell
rows=513, cols=257
==2130767== Conditional jump or move depends on uninitialised value(s)
==2130767==    at 0x83FDAAE: PCSetUp_MG (mg.c:998)
==2130767==    by 0x8620C04: PCSetUp (precon.c:1071)
==2130767==    by 0x7DA78D5: KSPSetUp (itfunc.c:415)
==2130767==    by 0x7DB2093: KSPSolve_Private (itfunc.c:826)
==2130767==    by 0x7DB7A53: KSPSolve (itfunc.c:1075)
==2130767==    by 0x10D2F7: main (ex65shell.c:79)
==2130767==
==2130767== Conditional jump or move depends on uninitialised value(s)
==2130767==    at 0x5794061: VecDestroy (vector.c:570)
==2130767==    by 0x83FDC36: PCSetUp_MG (mg.c:999)
==2130767==    by 0x8620C04: PCSetUp (precon.c:1071)
==2130767==    by 0x7DA78D5: KSPSetUp (itfunc.c:415)
==2130767==    by 0x7DB2093: KSPSolve_Private (itfunc.c:826)
==2130767==    by 0x7DB7A53: KSPSolve (itfunc.c:1075)
==2130767==    by 0x10D2F7: main (ex65shell.c:79)
==2130767==

We are clearly doing something wrong since PCSetUp_MG (mg.c:998) is an area of code where I wouldn't expect we would enter.

Can you advise on the proper way to achieve our goal?

Best regards

    Matteo

<ex65.patch>
-- 
Prof. Matteo Semplice
Università degli Studi dell’Insubria
Dipartimento di Scienza e Alta Tecnologia – DiSAT
Professore Associato
Via Valleggio, 11 – 22100 Como (CO) – Italia
tel.: +39 031 2386316