[petsc-users] Problem solving Ax=b with rectangular matrix A

Mon Sep 26 03:53:20 CDT 2022

The QR factorization from SuiteSparse is sequential only, cannot be used in parallel.
In parallel you can try PCBJACOBI with a PCQR local preconditioner.
Pierre may have additional suggestions.

Jose

> El 26 sept 2022, a las 10:47, fujisan <fujisan43 at gmail.com> escribió:
> 
> I did configure Petsc with the option --download-suitesparse.
> 
> The error is more like this:
> PETSC ERROR: Could not locate a solver type for factorization type QR and matrix type mpiaij.
> 
> Fuji
> 
> On Mon, Sep 26, 2022 at 10:25 AM Jose E. Roman <jroman at dsic.upv.es> wrote:
> If the error message is "Could not locate a solver type for factorization type QR" then you should configure PETSc with --download-suitesparse
> 
> Jose
> 
> 
> > El 26 sept 2022, a las 9:06, fujisan <fujisan43 at gmail.com> escribió:
> > 
> > Thank you Pierre,
> > 
> > I used PCNONE along with KSPLSQR and it worked.
> > But as for PCQR, it cannot be found. There is nothing about it in the documentation as well.
> > 
> > Fuji
> > 
> > On Wed, Sep 21, 2022 at 12:20 PM Pierre Jolivet <pierre at joliv.et> wrote:
> > Yes, but you need to use a KSP that handles rectangular Mat, such as KSPLSQR (-ksp_type lsqr).
> > PCLU does not handle rectangular Pmat. The only PC that handle rectangular Pmat are PCQR, PCNONE.
> > If you supply the normal equations as the Pmat for LSQR, then you can use “standard” PC.
> > You can have a look at https://petsc.org/main/src/ksp/ksp/tutorials/ex27.c.html that covers most of these cases.
> > 
> > Thanks,
> > Pierre
> > 
> > (sorry for the earlier answer sent wrongfully to petsc-maint, please discard the previous email)
> > 
> >> On 21 Sep 2022, at 10:03 AM, fujisan <fujisan43 at gmail.com> wrote:
> >> 
> >> I'm trying to solve Ax=b with a sparse rectangular matrix A (of size 33x17 in my test) using
> >> options '-ksp_type stcg -pc_type lu' on 1 or 2 cpus.
> >> 
> >> And I always get an error saying "Incompatible vector local lengths" (see below).
> >> 
> >> Here is the relevant lines of my code:
> >> 
> >> program test
> >>     ...
> >>     ! Variable declarations
> >> 
> >>     PetscCallA(PetscInitialize(PETSC_NULL_CHARACTER,ierr))
> >> 
> >>     PetscCall(MatCreate(PETSC_COMM_WORLD,A,ierr))
> >>     PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m,n,ierr))
> >>     PetscCall(MatSetType(A,MATMPIAIJ,ierr))
> >>     PetscCall(MatSetFromOptions(A,ierr))
> >>     PetscCall(MatSetUp(A,ierr))
> >>     PetscCall(MatGetOwnershipRange(A,istart,iend,ierr))
> >> 
> >>     do irow=istart,iend-1
> >>         ... Reading from file ...
> >>         PetscCall(MatSetValues(A,1,irow,nzv,col,val,ADD_VALUES,ierr))
> >>         ...
> >>     enddo
> >> 
> >>     PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr))
> >>     PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr))
> >>     
> >>     ! Creating vectors x and b
> >>     PetscCallA(MatCreateVecs(A,x,b,ierr))
> >> 
> >>     ! Duplicating x in u.
> >>     PetscCallA(VecDuplicate(x,u,ierr))
> >> 
> >>     ! u is used to calculate b
> >>     PetscCallA(VecSet(u,1.0,ierr))
> >> 
> >>     PetscCallA(VecAssemblyBegin(u,ierr))
> >>     PetscCallA(VecAssemblyEnd(u,ierr))
> >> 
> >>     ! Calculating Au = b
> >>     PetscCallA(MatMult(A,u,b,ierr)) ! A.u = b
> >> 
> >>     PetscCallA(KSPSetType(ksp,KSPCG,ierr))
> >> 
> >>     PetscCallA(KSPSetOperators(ksp,A,A,ierr))
> >> 
> >>     PetscCallA(KSPSetFromOptions(ksp,ierr))
> >> 
> >>     ! Solving Ax = b, x unknown
> >>     PetscCallA(KSPSolve(ksp,b,x,ierr))
> >> 
> >>     PetscCallA(VecDestroy(x,ierr))
> >>     PetscCallA(VecDestroy(u,ierr))
> >>     PetscCallA(VecDestroy(b,ierr))
> >>     PetscCallA(MatDestroy(A,ierr))
> >>     PetscCallA(KSPDestroy(ksp,ierr))
> >> 
> >>     call PetscFinalize(ierr)
> >> end program
> >> 
> >> The code reads a sparse matrix from a binary file.
> >> I also output the sizes of matrix A and vectors b, x, u.
> >> They all seem consistent.
> >> 
> >> What am I doing wrong?
> >> Is it possible to solve Ax=b with A rectangular?
> >> 
> >> Thank you in advance for your help.
> >> Have a nice day.
> >> 
> >> Fuji
> >> 
> >>  Matrix size : m=          33  n=          17  cpu size:            1
> >>  Size of matrix A  :           33          17
> >>  Size of vector b :           33
> >>  Size of vector x :           17
> >>  Size of vector u :           17
> >> [0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
> >> [0]PETSC ERROR: Arguments are incompatible
> >> [0]PETSC ERROR: Incompatible vector local lengths parameter # 1 local size 33 != parameter # 2 local size 17
> >> [0]PETSC ERROR: See https://petsc.org/release/faq/ for trouble shooting.
> >> [0]PETSC ERROR: Petsc Development GIT revision: v3.17.4-1341-g91b2b62a00  GIT Date: 2022-09-15 19:26:07 +0000
> >> [0]PETSC ERROR: ./bin/solve on a x86_64 named master by fujisan Tue Sep 20 16:56:37 2022
> >> [0]PETSC ERROR: Configure options --with-petsc-arch=x86_64 --COPTFLAGS="-g -O3" --FOPTFLAGS="-g -O3" --CXXOPTFLAGS="-g -O3" --with-debugging=0 --with-cc=mpiicc --with-cxx=mpiicpc --with-fc=mpiifort --with-single-library=1 --with-mpiexec=mpiexec --with-precision=double --with-fortran-interfaces=1 --with-make=1 --with-mpi=1 --with-mpi-compilers=1 --download-fblaslapack=0 --download-hypre=1 --download-cmake=0 --with-cmake=1 --download-metis=1 --download-parmetis=1 --download-ptscotch=0 --download-suitesparse=1 --download-triangle=1 --download-superlu=1 --download-superlu_dist=1 --download-scalapack=1 --download-mumps=1 --download-elemental=1 --download-spai=0 --download-parms=1 --download-moab=1 --download-chaco=0 --download-fftw=1 --with-petsc4py=1 --download-mpi4py=1 --download-saws --download-concurrencykit=1 --download-revolve=1 --download-cams=1 --download-p4est=0 --with-zlib=1 --download-mfem=1 --download-glvis=0 --with-opengl=0 --download-libpng=1 --download-libjpeg=1 --download-slepc=1 --download-hpddm=1 --download-bamg=1 --download-mmg=0 --download-parmmg=0 --download-htool=1 --download-egads=0 --download-opencascade=0 PETSC_ARCH=x86_64
> >> [0]PETSC ERROR: #1 VecCopy() at /data/softs/petsc/src/vec/vec/interface/vector.c:1607
> >> [0]PETSC ERROR: #2 KSPSolve_BiCG() at /data/softs/petsc/src/ksp/ksp/impls/bicg/bicg.c:40
> >> [0]PETSC ERROR: #3 KSPSolve_Private() at /data/softs/petsc/src/ksp/ksp/interface/itfunc.c:877
> >> [0]PETSC ERROR: #4 KSPSolve() at /data/softs/petsc/src/ksp/ksp/interface/itfunc.c:1048
> >> [0]PETSC ERROR: #5 solve.F90:218
> >> Abort(75) on node 0 (rank 0 in comm 16): application called MPI_Abort(MPI_COMM_SELF, 75) - process 0
> >> 
> > 
> 