Actual source code: ex15f.F90

petsc-master 2019-05-18
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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*/


 14: !
 15: !     -------------------------------------------------------------------------
 16: !
 17: !     Module contains diag needed by shell preconditioner
 18: !
 19:       module mymoduleex15f
 20:  #include <petsc/finclude/petscksp.h>
 21:       use petscksp
 22:       Vec    diag
 23:       end module

 25:       program main
 26:       use mymoduleex15f
 27:       implicit none

 29: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 30: !                   Variable declarations
 31: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 32: !
 33: !  Variables:
 34: !     ksp     - linear solver context
 35: !     ksp      - Krylov subspace method context
 36: !     pc       - preconditioner context
 37: !     x, b, u  - approx solution, right-hand-side, exact solution vectors
 38: !     A        - matrix that defines linear system
 39: !     its      - iterations for convergence
 40: !     norm     - norm of solution error

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

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

 56:       external SampleShellPCSetUp, SampleShellPCApply
 57:       external  SampleShellPCDestroy

 59: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 60: !                 Beginning of program
 61: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 63:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 64:       if (ierr .ne. 0) then
 65:         print*,'Unable to initialize PETSc'
 66:         stop
 67:       endif
 68:       one     = 1.0
 69:       neg_one = -1.0
 70:       i1 = 1
 71:       m       = 8
 72:       n       = 7
 73:       five    = 5
 74:       call PetscOptionsGetInt(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-m',m,flg,ierr)
 75:       call PetscOptionsGetInt(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-n',n,flg,ierr)
 76:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

 78: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 79: !      Compute the matrix and right-hand-side vector that define
 80: !      the linear system, Ax = b.
 81: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

 88:       call MatCreate(PETSC_COMM_WORLD,A,ierr)
 89:       call MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n,ierr)
 90:       call MatSetType(A, MATAIJ,ierr)
 91:       call MatSetFromOptions(A,ierr)
 92:       call MatMPIAIJSetPreallocation(A,five,PETSC_NULL_INTEGER,five,PETSC_NULL_INTEGER,ierr)
 93:       call MatSeqAIJSetPreallocation(A,five,PETSC_NULL_INTEGER,ierr)

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

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

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

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

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

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

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

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

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

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

160: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
161: !         Create the linear solver and set various options
162: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

164: !  Create linear solver context

166:       call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)

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

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

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

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

182: !
183: !  Set a user-defined shell preconditioner if desired
184: !
185:       call PetscOptionsHasName(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-user_defined_pc',user_defined_pc,ierr)

187:       if (user_defined_pc) then

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

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

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

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

201:       else
202:          call PCSetType(pc,PCJACOBI,ierr)
203:       endif

205: !  Set runtime options, e.g.,
206: !      -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
207: !  These options will override those specified above as long as
208: !  KSPSetFromOptions() is called _after_ any other customization
209: !  routines.

211:       call KSPSetFromOptions(ksp,ierr)

213: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
214: !                      Solve the linear system
215: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

219: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
220: !                     Check solution and clean up
221: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

223: !  Check the error

225:       call VecAXPY(x,neg_one,u,ierr)
226:       call VecNorm(x,NORM_2,norm,ierr)
227:       call KSPGetIterationNumber(ksp,its,ierr)

229:       if (rank .eq. 0) then
230:         if (norm .gt. 1.e-12) then
231:            write(6,100) norm,its
232:         else
233:            write(6,110) its
234:         endif
235:       endif
236:   100 format('Norm of error ',1pe11.4,' iterations ',i5)
237:   110 format('Norm of error < 1.e-12,iterations ',i5)

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

242:       call KSPDestroy(ksp,ierr)
243:       call VecDestroy(u,ierr)
244:       call VecDestroy(x,ierr)
245:       call VecDestroy(b,ierr)
246:       call MatDestroy(A,ierr)

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

250:       call PetscFinalize(ierr)
251:       end

253: !/***********************************************************************/
254: !/*          Routines for a user-defined shell preconditioner           */
255: !/***********************************************************************/

257: !
258: !   SampleShellPCSetUp - This routine sets up a user-defined
259: !   preconditioner context.
260: !
261: !   Input Parameters:
262: !   pc - preconditioner object
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,ierr)
274:       use mymoduleex15f
275:       use petscksp
276:       implicit none

278:       PC      pc
279:       Mat     pmat
280:       integer ierr

282:       call PCGetOperators(pc,PETSC_NULL_MAT,pmat,ierr)
283:       call MatCreateVecs(pmat,diag,PETSC_NULL_VEC,ierr)
284:       call MatGetDiagonal(pmat,diag,ierr)
285:       call VecReciprocal(diag,ierr)

287:       end

289: ! -------------------------------------------------------------------
290: !
291: !   SampleShellPCApply - This routine demonstrates the use of a
292: !   user-provided preconditioner.
293: !
294: !   Input Parameters:
295: !   pc - preconditioner object
296: !   x - input vector
297: !
298: !   Output Parameters:
299: !   y - preconditioned vector
300: !   ierr  - error code (nonzero if error has been detected)
301: !
302: !   Notes:
303: !   This code implements the Jacobi preconditioner, merely as an
304: !   example of working with a PCSHELL.  Note that the Jacobi method
305: !   is already provided within PETSc.
306: !
307:       subroutine SampleShellPCApply(pc,x,y,ierr)
308:       use mymoduleex15f
309:       implicit none

311:       PC      pc
312:       Vec     x,y
313:       integer ierr

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

317:       end

319: !/***********************************************************************/
320: !/*          Routines for a user-defined shell preconditioner           */
321: !/***********************************************************************/

323: !
324: !   SampleShellPCDestroy - This routine destroys (frees the memory of) any
325: !      objects we made for the preconditioner
326: !
327: !   Input Parameters:
328: !   pc - for this example we use the actual PC as our shell context
329: !
330: !   Output Parameter:
331: !   ierr  - error code (nonzero if error has been detected)
332: !

334:       subroutine SampleShellPCDestroy(pc,ierr)
335:       use mymoduleex15f
336:       implicit none

338:       PC      pc
339:       PetscErrorCode ierr

341: !  Normally we would recommend storing all the work data (like diag) in
342: !  the context set with PCShellSetContext()

344:       call VecDestroy(diag,ierr)

346:       end

348: !
349: !/*TEST
350: !
351: !   test:
352: !      nsize: 2
353: !      args: -ksp_view -user_defined_pc -ksp_gmres_cgs_refinement_type refine_always
354: !
355: !TEST*/