[petsc-users] Customizing NASM subsnes

[Barry Smith]

     MPI_Comm_size(PETSC_COMM_WORLD,&size);
     MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
> SNESNASMGetSNES(snes,0,&subsnes);
>  char prefix[10];
>  sprintf(prefix,"sub_%d_",rank);
>  SNESSetOptionsPrefix(subsnes,prefix);



> On Jun 17, 2022, at 9:35 AM, Matthew Knepley <knepley at gmail.com> wrote:
> 
> On Fri, Jun 17, 2022 at 9:22 AM Takahashi, Tadanaga <tt73 at njit.edu <mailto:tt73 at njit.edu>> wrote:
> I'm having some trouble pulling out the subsolver. I tried to use SNESNASMGetSNES in a loop over each subdomain. However I get an error when I run the code with more than one MPI processors. Here is a snippet from my code: 
> 
>    SNES           snes, subsnes;
>    PetscMPIInt    rank, size;
>    ... 
>    ierr = SNESCreate(PETSC_COMM_WORLD,&snes); CHKERRQ(ierr);
>    ierr = SNESSetType(snes,SNESNASM); CHKERRQ(ierr);
>    ierr = SNESNASMSetType(snes,PC_ASM_RESTRICT); CHKERRQ(ierr);
>    ... 
>    ierr = SNESSetFromOptions(snes); CHKERRQ(ierr);
>    ierr = SNESSetUp(snes); CHKERRQ(ierr);
>    PetscPrintf(PETSC_COMM_WORLD, "Size = %d\n",size);
>    for (i=0; i<size; i++) {
>       PetscPrintf(PETSC_COMM_WORLD, "rank = %d\n",i);
>       SNESNASMGetSNES(snes,i,&subsnes);
>       // char prefix[10];
>       // sprintf(prefix,"sub_%d_",i);
>       // SNESSetOptionsPrefix(subsnes,prefix);
>    }
>    ... 
>    ierr = SNESSolve(snes,NULL,u_initial); CHKERRQ(ierr);
> 
> 
> And, here is the output of the code when I run with 2 MPI procs: 
> 
> SNESNASMGetSNES() gets the local subsolvers. It seems you only have one per process.
> You can check https://petsc.org/main/docs/manualpages/SNES/SNESNASMGetNumber/ <https://petsc.org/main/docs/manualpages/SNES/SNESNASMGetNumber/>
> 
> Notice that your current code will not work because, according to your explanation, you only want to change
> the prefix on a single rank, so you need to check the rank when you do it.
> 
>   Thanks,
> 
>      Matt
>  
> takahashi at ubuntu:~/Desktop/MA-DDM/C/Rectangle$ mpiexec -n 2 ./test1
> Size = 2
> rank = 0
> rank = 1
> [0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> [0]PETSC ERROR: Argument out of range
> [0]PETSC ERROR: No such subsolver
> [0]PETSC ERROR: See https://petsc.org/release/faq/ <https://petsc.org/release/faq/> for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.17.1, unknown 
> [0]PETSC ERROR: ./test1 on a linux-gnu-c-debug named ubuntu by takahashi Fri Jun 17 06:06:38 2022
> [0]PETSC ERROR: Configure options --with-mpi-dir=/usr --with-fc=0
> [0]PETSC ERROR: #1 SNESNASMGetSNES() at /home/takahashi/Desktop/petsc/src/snes/impls/nasm/nasm.c:923
> 
> ===================================================================================
> =   BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES
> =   RANK 0 PID 976566 RUNNING AT ubuntu
> =   KILLED BY SIGNAL: 9 (Killed)
> ===================================================================================
> 
> This error doesn't occur when I run this without MPI. However, I tried to change the prefix of the subdomain to `sub_0_` but I am not able to change the snes_type using this prefix. Running ./test1 -snes_view -help | grep sub_0_snes_type prints nothing. 
> 
> On Thu, Jun 16, 2022 at 6:23 PM Matthew Knepley <knepley at gmail.com <mailto:knepley at gmail.com>> wrote:
> On Thu, Jun 16, 2022 at 5:57 PM tt73 <tt73 at njit.edu <mailto:tt73 at njit.edu>> wrote:
> 
> Hi, 
> 
> I am using  NASM as the outer solver for a nonlinear problem. For one of the subdomains, I want to run the local solve with a different set of options form the others. Is there any way to set options for each subdomain? 
> 
> I can see two ways:
> 
>   1) Pull out the subsolver and set it using the API
> 
>   2) Pull out the subsolver and give it a different prefix
> 
>   Thanks,
> 
>      Matt
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener
> 
> https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener
> 
> https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>

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