[petsc-users] MatCreateTranspose

[Zhang, Hong]

Carl-Johan,
You can use MatSolveTranspose() to solve A'*x = b. See petsc/src/ksp/ksp/tutorials/ex79.c

`MatCreateTranspose()` is used if you only need a matrix that behaves like the transpose, but don't need the storage to be changed, i.e., A and A' share same matrix storage, thus MatGetRow() needs to get columns of A, which is not supported.

Hong
________________________________
From: petsc-users <petsc-users-bounces at mcs.anl.gov> on behalf of Carl-Johan Thore <carljohanthore at gmail.com>
Sent: Tuesday, April 9, 2024 6:38 AM
To: petsc-users <petsc-users at mcs.anl.gov>
Subject: [petsc-users] MatCreateTranspose

Hi, I have a matrix A with transpose A' and would like to solve the linear system A'*x = b using the pcredistribute preconditioner. It seemed like a good idea to use MatCreateTranspose, but this leads to [0]PETSC ERROR: ---------------------
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Hi,

I have a matrix A with transpose A' and would like to solve the linear system A'*x = b using the pcredistribute preconditioner. It seemed like a good idea to use MatCreateTranspose, but this leads to

[0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
[0]PETSC ERROR: No support for this operation for this object type
[0]PETSC ERROR: No method getrow for Mat of type transpose
[0]PETSC ERROR: See https://urldefense.us/v3/__https://petsc.org/release/faq/__;!!G_uCfscf7eWS!ZjJecuElTk9FpHCmWARWcvLbSCiWXeEshhB3Z61WIK2V0KX6gOTrfRK8nMlqoZ8Q7Q1y7I3VGWH_MP7gYz7pNt0l$ <https://urldefense.us/v3/__https://petsc.org/release/faq/__;!!G_uCfscf7eWS!bVYrcPfbXSXCcthSH37OClTgnf7RxkizULEW1ZZJ5yYG3-50366x_OFSPmOgGWEcOeFyOmAMSFewAyCnxIUg7K8W_neRPw$> for trouble shooting.
[0]PETSC ERROR: Petsc Release Version 3.21.0, unknown
[0]PETSC ERROR: Configure options COPTFLAGS="-O3 -march=native" CXXOPTFLAGS="-O3 -march=native" --with-fortran-bindings=0 FOPTFLAGS="-O3 -march=native" CUDAOPTFLAGS=-O3 --with-cuda --with-cusp --with-debugging=0 --download-scalapack --download-hdf5 --download-zlib --download-mumps --download-parmetis --download-metis --download-ptscotch --download-hypre --download-spai
[0]PETSC ERROR: #1 MatGetRow() at /mnt/c/mathware/petsc/petsc-v3-21-0/src/mat/interface/matrix.c:573
[0]PETSC ERROR: #2 PCSetUp_Redistribute() at /mnt/c/mathware/petsc/petsc-v3-21-0/src/ksp/pc/impls/redistribute/redistribute.c:111
[0]PETSC ERROR: #3 PCSetUp() at /mnt/c/mathware/petsc/petsc-v3-21-0/src/ksp/pc/interface/precon.c:1079
[0]PETSC ERROR: #4 KSPSetUp() at /mnt/c/mathware/petsc/petsc-v3-21-0/src/ksp/ksp/interface/itfunc.c:415

MatTranspose is a working alternative, but MatCreateTranspose would be preferable. In principle the solution seems straightforward -- just add a getrow method -- but is it, and is it a good idea (performancewise etc)?

Kind regards,
Carl-Johan
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