Actual source code: ex21f.F
petsc-3.4.2 2013-07-02

      1: !
      2: !   Solves a linear system in parallel with KSP.  Also indicates
      3: !   use of a user-provided preconditioner.  Input parameters include:
      4: !
      5: !
      6: !/*T
      7: !   Concepts: KSP^basic parallel example
      8: !   Concepts: PC^setting a user-defined shell preconditioner
      9: !   Processors: n
     10: !T*/
     11: !
     12: !  -------------------------------------------------------------------------

     14:       program main
     15:       implicit none

     17: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     18: !                    Include files
     19: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     20: !
     21: !     petscsys.h  - base PETSc routines      petscvec.h - vectors
     22: !     petscmat.h - matrices
     23: !     petscksp.h    - Krylov subspace methods  petscpc.h  - preconditioners

     25: #include <finclude/petscsys.h>
     26: #include <finclude/petscvec.h>
     27: #include <finclude/petscmat.h>
     28: #include <finclude/petscpc.h>
     29: #include <finclude/petscksp.h>

     31: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     32: !                   Variable declarations
     33: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     34: !
     35: !  Variables:
     36: !     ksp     - linear solver context
     37: !     ksp      - Krylov subspace method context
     38: !     pc       - preconditioner context
     39: !     x, b, u  - approx solution, right-hand-side, exact solution vectors
     40: !     A        - matrix that defines linear system
     41: !     its      - iterations for convergence
     42: !     norm     - norm of solution error

     44:       Vec              x,b,u
     45:       Mat              A
     46:       PC               pc
     47:       KSP              ksp
     48:       PetscScalar      v,one,neg_one
     49:       double precision norm,tol
     50:       PetscInt i,j,II,JJ,Istart
     51:       PetscInt Iend,m,n,its,ione
     52:       PetscMPIInt rank
     53:       PetscBool  flg
     54:       PetscErrorCode ierr

     56: !  Note: Any user-defined Fortran routines MUST be declared as external.

     58:       external SampleShellPCSetUp,SampleShellPCApply

     60: !  Common block to store data for user-provided preconditioner
     61:       common /mypcs/ jacobi,sor,work
     62:       PC jacobi,sor
     63:       Vec work

     65: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     66: !                 Beginning of program
     67: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     69:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
     70:       one     = 1.0
     71:       neg_one = -1.0
     72:       m       = 8
     73:       n       = 7
     74:       ione    = 1
     75:       call PetscOptionsGetInt(PETSC_NULL_CHARACTER,'-m',m,flg,ierr)
     76:       call PetscOptionsGetInt(PETSC_NULL_CHARACTER,'-n',n,flg,ierr)
     77:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

     79: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     80: !      Compute the matrix and right-hand-side vector that define
     81: !      the linear system, Ax = b.
     82: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

     84: !  Create parallel matrix, specifying only its global dimensions.
     85: !  When using MatCreate(), the matrix format can be specified at
     86: !  runtime. Also, the parallel partitioning of the matrix is
     87: !  determined by PETSc at runtime.

     89:       call MatCreate(PETSC_COMM_WORLD,A,ierr)
     90:       call MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n,ierr)
     91:       call MatSetFromOptions(A,ierr)
     92:       call MatSetUp(A,ierr)

     94: !  Currently, all PETSc parallel matrix formats are partitioned by
     95: !  contiguous chunks of rows across the processors.  Determine which
     96: !  rows of the matrix are locally owned.

     98:       call MatGetOwnershipRange(A,Istart,Iend,ierr)

    100: !  Set matrix elements for the 2-D, five-point stencil in parallel.
    101: !   - Each processor needs to insert only elements that it owns
    102: !     locally (but any non-local elements will be sent to the
    103: !     appropriate processor during matrix assembly).
    104: !   - Always specify global row and columns of matrix entries.
    105: !   - Note that MatSetValues() uses 0-based row and column numbers
    106: !     in Fortran as well as in C.

    108:       do 10, II=Istart,Iend-1
    109:         v = -1.0
    110:         i = II/n
    111:         j = II - i*n
    112:         if (i.gt.0) then
    113:           JJ = II - n
    114:           call MatSetValues(A,ione,II,ione,JJ,v,ADD_VALUES,ierr)
    115:         endif
    116:         if (i.lt.m-1) then
    117:           JJ = II + n
    118:           call MatSetValues(A,ione,II,ione,JJ,v,ADD_VALUES,ierr)
    119:         endif
    120:         if (j.gt.0) then
    121:           JJ = II - 1
    122:           call MatSetValues(A,ione,II,ione,JJ,v,ADD_VALUES,ierr)
    123:         endif
    124:         if (j.lt.n-1) then
    125:           JJ = II + 1
    126:           call MatSetValues(A,ione,II,ione,JJ,v,ADD_VALUES,ierr)
    127:         endif
    128:         v = 4.0
    129:         call  MatSetValues(A,ione,II,ione,II,v,ADD_VALUES,ierr)
    130:  10   continue

    132: !  Assemble matrix, using the 2-step process:
    133: !       MatAssemblyBegin(), MatAssemblyEnd()
    134: !  Computations can be done while messages are in transition,
    135: !  by placing code between these two statements.

    137:       call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr)
    138:       call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr)

    140: !  Create parallel vectors.
    141: !   - Here, the parallel partitioning of the vector is determined by
    142: !     PETSc at runtime.  We could also specify the local dimensions
    143: !     if desired -- or use the more general routine VecCreate().
    144: !   - When solving a linear system, the vectors and matrices MUST
    145: !     be partitioned accordingly.  PETSc automatically generates
    146: !     appropriately partitioned matrices and vectors when MatCreate()
    147: !     and VecCreate() are used with the same communicator.
    148: !   - Note: We form 1 vector from scratch and then duplicate as needed.

    150:       call VecCreateMPI(PETSC_COMM_WORLD,PETSC_DECIDE,m*n,u,ierr)
    151:       call VecDuplicate(u,b,ierr)
    152:       call VecDuplicate(b,x,ierr)

    154: !  Set exact solution; then compute right-hand-side vector.

    156:       call VecSet(u,one,ierr)
    157:       call MatMult(A,u,b,ierr)

    159: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    160: !         Create the linear solver and set various options
    161: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    163: !  Create linear solver context

    165:       call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)

    167: !  Set operators. Here the matrix that defines the linear system
    168: !  also serves as the preconditioning matrix.

    170:       call KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN,ierr)

    172: !  Set linear solver defaults for this problem (optional).
    173: !   - By extracting the KSP and PC contexts from the KSP context,
    174: !     we can then directly directly call any KSP and PC routines
    175: !     to set various options.

    177:       call KSPGetPC(ksp,pc,ierr)
    178:       tol = 1.e-7
    179:       call KSPSetTolerances(ksp,tol,PETSC_DEFAULT_DOUBLE_PRECISION,     &
    180:      &     PETSC_DEFAULT_DOUBLE_PRECISION,PETSC_DEFAULT_INTEGER,ierr)

    182: !
    183: !  Set a user-defined shell preconditioner
    184: !

    186: !  (Required) Indicate to PETSc that we are using a shell preconditioner
    187:       call PCSetType(pc,PCSHELL,ierr)

    189: !  (Required) Set the user-defined routine for applying the preconditioner
    190:       call PCShellSetApply(pc,SampleShellPCApply,ierr)

    192: !  (Optional) Do any setup required for the preconditioner
    193: !     Note: if you use PCShellSetSetUp, this will be done for your
    194:       call SampleShellPCSetUp(pc,x,ierr)

    197: !  Set runtime options, e.g.,
    198: !      -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
    199: !  These options will override those specified above as long as
    200: !  KSPSetFromOptions() is called _after_ any other customization
    201: !  routines.

    203:       call KSPSetFromOptions(ksp,ierr)

    205: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    206: !                      Solve the linear system
    207: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    209:       call KSPSolve(ksp,b,x,ierr)

    211: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    212: !                     Check solution and clean up
    213: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    215: !  Check the error

    217:       call VecAXPY(x,neg_one,u,ierr)
    218:       call VecNorm(x,NORM_2,norm,ierr)
    219:       call KSPGetIterationNumber(ksp,its,ierr)

    221:       if (rank .eq. 0) then
    222:         if (norm .gt. 1.e-12) then
    223:            write(6,100) norm,its
    224:         else
    225:            write(6,110) its
    226:         endif
    227:       endif
    228:   100 format('Norm of error ',1pe11.4,' iterations ',i5)
    229:   110 format('Norm of error < 1.e-12,iterations ',i5)

    232: !  Free work space.  All PETSc objects should be destroyed when they
    233: !  are no longer needed.

    235:       call KSPDestroy(ksp,ierr)
    236:       call VecDestroy(u,ierr)
    237:       call VecDestroy(x,ierr)
    238:       call VecDestroy(b,ierr)
    239:       call MatDestroy(A,ierr)

    241: ! Free up PCShell data
    242:       call PCDestroy(sor,ierr)
    243:       call PCDestroy(jacobi,ierr)
    244:       call VecDestroy(work,ierr)

    247: !  Always call PetscFinalize() before exiting a program.

    249:       call PetscFinalize(ierr)
    250:       end

    252: !/***********************************************************************/
    253: !/*          Routines for a user-defined shell preconditioner           */
    254: !/***********************************************************************/

    256: !
    257: !   SampleShellPCSetUp - This routine sets up a user-defined
    258: !   preconditioner context.
    259: !
    260: !   Input Parameters:
    261: !   pc    - preconditioner object
    262: !   x     - vector
    263: !
    264: !   Output Parameter:
    265: !   ierr  - error code (nonzero if error has been detected)
    266: !
    267: !   Notes:
    268: !   In this example, we define the shell preconditioner to be Jacobi
    269: !   method.  Thus, here we create a work vector for storing the reciprocal
    270: !   of the diagonal of the preconditioner matrix; this vector is then
    271: !   used within the routine SampleShellPCApply().
    272: !
    273:       subroutine SampleShellPCSetUp(pc,x,ierr)

    275:       implicit none

    277: #include <finclude/petscsys.h>
    278: #include <finclude/petscvec.h>
    279: #include <finclude/petscmat.h>

    281:       PC      pc
    282:       Vec     x
    283:       Mat     pmat
    284:       PetscErrorCode ierr

    286: !  Common block to store data for user-provided preconditioner
    287:       common /mypcs/ jacobi,sor,work
    288:       PC jacobi,sor
    289:       Vec work

    291:       call PCGetOperators(pc,PETSC_NULL_OBJECT,pmat,PETSC_NULL_INTEGER,  &
    292:      &                     ierr)
    293:       call PCCreate(PETSC_COMM_WORLD,jacobi,ierr)
    294:       call PCSetType(jacobi,PCJACOBI,ierr)
    295:       call PCSetOperators(jacobi,pmat,pmat,DIFFERENT_NONZERO_PATTERN,    &
    296:      &                     ierr)
    297:       call PCSetUp(jacobi,ierr)

    299:       call PCCreate(PETSC_COMM_WORLD,sor,ierr)
    300:       call PCSetType(sor,PCSOR,ierr)
    301:       call PCSetOperators(sor,pmat,pmat,DIFFERENT_NONZERO_PATTERN,       &
    302:      &                     ierr)
    303: !      call PCSORSetSymmetric(sor,SOR_LOCAL_SYMMETRIC_SWEEP,ierr)
    304:       call PCSetUp(sor,ierr)

    306:       call VecDuplicate(x,work,ierr)

    308:       end

    310: ! -------------------------------------------------------------------
    311: !
    312: !   SampleShellPCApply - This routine demonstrates the use of a
    313: !   user-provided preconditioner.
    314: !
    315: !   Input Parameters:
    316: !   pc - preconditioner object
    317: !   x - input vector
    318: !
    319: !   Output Parameters:
    320: !   y - preconditioned vector
    321: !   ierr  - error code (nonzero if error has been detected)
    322: !
    323: !   Notes:
    324: !   This code implements the Jacobi preconditioner plus the
    325: !   SOR preconditioner
    326: !
    327: ! YOU CAN GET THE EXACT SAME EFFECT WITH THE PCCOMPOSITE preconditioner using
    328: ! mpiexec -n 1 ex21f -ksp_monitor -pc_type composite -pc_composite_pcs jacobi,sor -pc_composite_type additive
    329: !
    330:       subroutine SampleShellPCApply(pc,x,y,ierr)

    332:       implicit none

    334: #include <finclude/petscsys.h>
    335: #include <finclude/petscvec.h>
    336: #include <finclude/petscpc.h>

    338:       PC      pc
    339:       Vec     x,y
    340:       PetscErrorCode ierr
    341:       PetscScalar  one

    343: !  Common block to store data for user-provided preconditioner
    344:       common /mypcs/ jacobi,sor,work
    345:       PC  jacobi,sor
    346:       Vec work

    348:       one = 1.0
    349:       call PCApply(jacobi,x,y,ierr)
    350:       call PCApply(sor,x,work,ierr)
    351:       call VecAXPY(y,one,work,ierr)

    353:       end