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