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

Mon Sep 26 03:25:02 CDT 2022

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
>> 
>