Actual source code: ex15f.F

petsc-master 2014-12-24
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  1: !
  2: !   Solves a linear system in parallel with KSP.  Also indicates
  3: !   use of a user-provided preconditioner.  Input parameters include:
  4: !      -user_defined_pc : Activate a user-defined preconditioner
  5: !
  6: !
  7: !/*T
  8: !   Concepts: KSP^basic parallel example
  9: !   Concepts: PC^setting a user-defined shell preconditioner
 10: !   Processors: n
 11: !T*/
 12: !
 13: !  -------------------------------------------------------------------------

 15:       program main
 16:       implicit none

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

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

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

 45:       Vec              x,b,u
 46:       Mat              A
 47:       PC               pc
 48:       KSP              ksp
 49:       PetscScalar      v,one,neg_one
 50:       PetscReal norm,tol
 51:       PetscErrorCode ierr
 52:       PetscInt   i,j,II,JJ,Istart
 53:       PetscInt   Iend,m,n,i1,its,five
 54:       PetscMPIInt rank
 55:       PetscBool  user_defined_pc,flg

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

 59:       external SampleShellPCSetUp, SampleShellPCApply
 60:       external  SampleShellPCDestroy

 62: !  Common block to store data for user-provided preconditioner
 63:       common /myshellpc/ diag
 64:       Vec    diag

 66: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 67: !                 Beginning of program
 68: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 70:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 71:       one     = 1.0
 72:       neg_one = -1.0
 73:       i1 = 1
 74:       m       = 8
 75:       n       = 7
 76:       five    = 5
 77:       call PetscOptionsGetInt(PETSC_NULL_CHARACTER,'-m',m,flg,ierr)
 78:       call PetscOptionsGetInt(PETSC_NULL_CHARACTER,'-n',n,flg,ierr)
 79:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

 81: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 82: !      Compute the matrix and right-hand-side vector that define
 83: !      the linear system, Ax = b.
 84: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

 91:       call MatCreate(PETSC_COMM_WORLD,A,ierr)
 92:       call MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n,ierr)
 93:       call MatSetType(A, MATAIJ,ierr)
 94:       call MatSetFromOptions(A,ierr)
 95:       call MatMPIAIJSetPreallocation(A,five,PETSC_NULL_INTEGER,five,            &
 96:      &                     PETSC_NULL_INTEGER,ierr)
 97:       call MatSeqAIJSetPreallocation(A,five,PETSC_NULL_INTEGER,ierr)

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

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

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

113:       do 10, II=Istart,Iend-1
114:         v = -1.0
115:         i = II/n
116:         j = II - i*n
117:         if (i.gt.0) then
118:           JJ = II - n
119:           call MatSetValues(A,i1,II,i1,JJ,v,ADD_VALUES,ierr)
120:         endif
121:         if (i.lt.m-1) then
122:           JJ = II + n
123:           call MatSetValues(A,i1,II,i1,JJ,v,ADD_VALUES,ierr)
124:         endif
125:         if (j.gt.0) then
126:           JJ = II - 1
127:           call MatSetValues(A,i1,II,i1,JJ,v,ADD_VALUES,ierr)
128:         endif
129:         if (j.lt.n-1) then
130:           JJ = II + 1
131:           call MatSetValues(A,i1,II,i1,JJ,v,ADD_VALUES,ierr)
132:         endif
133:         v = 4.0
134:         call  MatSetValues(A,i1,II,i1,II,v,ADD_VALUES,ierr)
135:  10   continue

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

142:       call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr)
143:       call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr)

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

155:       call VecCreateMPI(PETSC_COMM_WORLD,PETSC_DECIDE,m*n,u,ierr)
156:       call VecDuplicate(u,b,ierr)
157:       call VecDuplicate(b,x,ierr)

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

161:       call VecSet(u,one,ierr)
162:       call MatMult(A,u,b,ierr)

164: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
165: !         Create the linear solver and set various options
166: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

168: !  Create linear solver context

170:       call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)

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

175:       call KSPSetOperators(ksp,A,A,ierr)

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

182:       call KSPGetPC(ksp,pc,ierr)
183:       tol = 1.e-7
184:       call KSPSetTolerances(ksp,tol,PETSC_DEFAULT_REAL,                       &
185:      &     PETSC_DEFAULT_REAL,PETSC_DEFAULT_INTEGER,ierr)

187: !
188: !  Set a user-defined shell preconditioner if desired
189: !
190:       call PetscOptionsHasName(PETSC_NULL_CHARACTER,'-user_defined_pc',      &
191:      &                    user_defined_pc,ierr)

193:       if (user_defined_pc) then

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

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

201: !  (Optional) Do any setup required for the preconditioner
202:          call PCShellSetSetUp(pc,SampleShellPCSetUp,ierr)

204: !  (Optional) Frees any objects we created for the preconditioner
205:          call PCShellSetDestroy(pc,SampleShellPCDestroy,ierr)

207:       else
208:          call PCSetType(pc,PCJACOBI,ierr)
209:       endif

211: !  Set runtime options, e.g.,
212: !      -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
213: !  These options will override those specified above as long as
214: !  KSPSetFromOptions() is called _after_ any other customization
215: !  routines.

217:       call KSPSetFromOptions(ksp,ierr)

219: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
220: !                      Solve the linear system
221: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

225: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
226: !                     Check solution and clean up
227: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

229: !  Check the error

231:       call VecAXPY(x,neg_one,u,ierr)
232:       call VecNorm(x,NORM_2,norm,ierr)
233:       call KSPGetIterationNumber(ksp,its,ierr)

235:       if (rank .eq. 0) then
236:         if (norm .gt. 1.e-12) then
237:            write(6,100) norm,its
238:         else
239:            write(6,110) its
240:         endif
241:       endif
242:   100 format('Norm of error ',1pe11.4,' iterations ',i5)
243:   110 format('Norm of error < 1.e-12,iterations ',i5)

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

248:       call KSPDestroy(ksp,ierr)
249:       call VecDestroy(u,ierr)
250:       call VecDestroy(x,ierr)
251:       call VecDestroy(b,ierr)
252:       call MatDestroy(A,ierr)

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

256:       call PetscFinalize(ierr)
257:       end

259: !/***********************************************************************/
260: !/*          Routines for a user-defined shell preconditioner           */
261: !/***********************************************************************/

263: !
264: !   SampleShellPCSetUp - This routine sets up a user-defined
265: !   preconditioner context.
266: !
267: !   Input Parameters:
268: !   pc - preconditioner object
269: !
270: !   Output Parameter:
271: !   ierr  - error code (nonzero if error has been detected)
272: !
273: !   Notes:
274: !   In this example, we define the shell preconditioner to be Jacobi
275: !   method.  Thus, here we create a work vector for storing the reciprocal
276: !   of the diagonal of the preconditioner matrix; this vector is then
277: !   used within the routine SampleShellPCApply().
278: !
279:       subroutine SampleShellPCSetUp(pc,ierr)

281:       implicit none

283: #include <finclude/petscsys.h>
284: #include <finclude/petscvec.h>
285: #include <finclude/petscmat.h>
286:       PC      pc

288:       Mat     pmat
289:       integer ierr

291: !  Common block to store data for user-provided preconditioner
292: !  Normally we would recommend storing all the work data (like diag) in
293: !  the context set with PCShellSetContext()

295:       common /myshellpc/ diag
296:       Vec    diag

298:       call PCGetOperators(pc,PETSC_NULL_OBJECT,pmat,ierr)
299:       call MatCreateVecs(pmat,diag,PETSC_NULL_OBJECT,ierr)
300:       call MatGetDiagonal(pmat,diag,ierr)
301:       call VecReciprocal(diag,ierr)

303:       end

305: ! -------------------------------------------------------------------
306: !
307: !   SampleShellPCApply - This routine demonstrates the use of a
308: !   user-provided preconditioner.
309: !
310: !   Input Parameters:
311: !   pc - preconditioner object
312: !   x - input vector
313: !
314: !   Output Parameters:
315: !   y - preconditioned vector
316: !   ierr  - error code (nonzero if error has been detected)
317: !
318: !   Notes:
319: !   This code implements the Jacobi preconditioner, merely as an
320: !   example of working with a PCSHELL.  Note that the Jacobi method
321: !   is already provided within PETSc.
322: !
323:       subroutine SampleShellPCApply(pc,x,y,ierr)

325:       implicit none

327: #include <finclude/petscsys.h>
328: #include <finclude/petscvec.h>

330:       PC      pc
331:       Vec     x,y
332:       integer ierr

334: !  Common block to store data for user-provided preconditioner
335:       common /myshellpc/ diag
336:       Vec    diag

338:       call VecPointwiseMult(y,x,diag,ierr)

340:       end

342: !/***********************************************************************/
343: !/*          Routines for a user-defined shell preconditioner           */
344: !/***********************************************************************/

346: !
347: !   SampleShellPCDestroy - This routine destroys (frees the memory of) any
348: !      objects we made for the preconditioner
349: !
350: !   Input Parameters:
351: !   pc - for this example we use the actual PC as our shell context
352: !
353: !   Output Parameter:
354: !   ierr  - error code (nonzero if error has been detected)
355: !

357:       subroutine SampleShellPCDestroy(pc,ierr)

359:       implicit none

361: #include <finclude/petscsys.h>
362: #include <finclude/petscvec.h>
363: #include <finclude/petscmat.h>
364:       PC      pc
365:       PetscErrorCode ierr

367: !  Common block to store data for user-provided preconditioner
368: !  Normally we would recommend storing all the work data (like diag) in
369: !  the context set with PCShellSetContext()

371:       common /myshellpc/ diag
372:       Vec    diag

374:       call VecDestroy(diag,ierr)

376:       end