Actual source code: ex5f.F

  1: ! "$Id: ex5f.F,v 1.80 2001/08/24 16:23:36 bsmith Exp $";
  2: !
  3: !  Description: This example solves a nonlinear system in parallel with SNES.
  4: !  We solve the  Bratu (SFI - solid fuel ignition) problem in a 2D rectangular
  5: !  domain, using distributed arrays (DAs) to partition the parallel grid.
  6: !  The command line options include:
  7: !    -par <param>, where <param> indicates the nonlinearity of the problem
  8: !       problem SFI:  <parameter> = Bratu parameter (0 <= par <= 6.81)
  9: !
 10: !  Program usage:  mpirun -np <procs> ex5f [-help] [all PETSc options]
 11: !
 12: !/*T
 13: !  Concepts: SNES^parallel Bratu example
 14: !  Concepts: DA^using distributed arrays;
 15: !  Processors: n
 16: !T*/
 17: !
 18: !  --------------------------------------------------------------------------
 19: !
 20: !  Solid Fuel Ignition (SFI) problem.  This problem is modeled by
 21: !  the partial differential equation
 22: !
 23: !          -Laplacian u - lambda*exp(u) = 0,  0 < x,y < 1,
 24: !
 25: !  with boundary conditions
 26: !
 27: !           u = 0  for  x = 0, x = 1, y = 0, y = 1.
 28: !
 29: !  A finite difference approximation with the usual 5-point stencil
 30: !  is used to discretize the boundary value problem to obtain a nonlinear
 31: !  system of equations.
 32: !
 33: !  --------------------------------------------------------------------------

 35:       program main
 36:       implicit none
 37: !
 38: !  We place common blocks, variable declarations, and other include files
 39: !  needed for this code in the single file ex5f.h.  We then need to include
 40: !  only this file throughout the various routines in this program.  See
 41: !  additional comments in the file ex5f.h.
 42: !
 43: #include "ex5f.h"

 45: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 46: !                   Variable declarations
 47: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 48: !
 49: !  Variables:
 50: !     snes        - nonlinear solver
 51: !     x, r        - solution, residual vectors
 52: !     J           - Jacobian matrix
 53: !     its         - iterations for convergence
 54: !
 55: !  See additional variable declarations in the file ex5f.h
 56: !
 57:       SNES                   snes
 58:       Vec                    x,r
 59:       Mat                    J,A
 60:       integer                its,flg,ierr
 61:       double precision       lambda_max,lambda_min
 62:       ISColoring             coloring
 63:       PetscTruth             adifor_jacobian,adiformf_jacobian

 65: !  Note: Any user-defined Fortran routines (such as FormJacobianLocal)
 66: !  MUST be declared as external.

 68:       external FormInitialGuess
 69:       external FormFunctionLocal,FormJacobianLocal
 70: #if defined(PETSC_HAVE_ADIFOR)
 71:       external g_FormFunctionLocal,m_FormFunctionLocal
 72: #endif

 74: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 75: !  Initialize program
 76: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 78:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 79:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
 80:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

 82: !  Initialize problem parameters

 84:       lambda_max = 6.81
 85:       lambda_min = 0.0
 86:       lambda     = 6.0
 87:       call PetscOptionsGetReal(PETSC_NULL_CHARACTER,'-par',lambda,                &
 88:      &                           flg,ierr)
 89:       if (lambda .ge. lambda_max .or. lambda .le. lambda_min) then
 90:          if (rank .eq. 0) write(6,*) 'Lambda is out of range'
 91:          SETERRQ(1,' ',ierr)
 92:       endif

 94: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 95: !  Create nonlinear solver context
 96: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 98:       call SNESCreate(PETSC_COMM_WORLD,snes,ierr)

100: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
101: !  Create vector data structures; set function evaluation routine
102: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

104: !  Create distributed array (DA) to manage parallel grid and vectors

106: ! This really needs only the star-type stencil, but we use the box
107: ! stencil temporarily.
108:       call DACreate2d(PETSC_COMM_WORLD,DA_NONPERIODIC,DA_STENCIL_BOX,-4,          &
109:      &     -4,PETSC_DECIDE,PETSC_DECIDE,1,1,PETSC_NULL_INTEGER,                   &
110:      &     PETSC_NULL_INTEGER,da,ierr)

112: !  Extract global and local vectors from DA; then duplicate for remaining
113: !  vectors that are the same types

115:       call DACreateGlobalVector(da,x,ierr)
116:       call VecDuplicate(x,r,ierr)

118: !  Get local grid boundaries (for 2-dimensional DA)

120:       call DAGetInfo(da,PETSC_NULL_INTEGER,mx,my,PETSC_NULL_INTEGER,            &
121:      &               PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,                     &
122:      &               PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,                     &
123:      &               PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,                     &
124:      &               PETSC_NULL_INTEGER,ierr)
125:       call DAGetCorners(da,xs,ys,PETSC_NULL_INTEGER,xm,ym,                      &
126:      &     PETSC_NULL_INTEGER,ierr)
127:       call DAGetGhostCorners(da,gxs,gys,PETSC_NULL_INTEGER,gxm,gym,             &
128:      &     PETSC_NULL_INTEGER,ierr)

130: !  Here we shift the starting indices up by one so that we can easily
131: !  use the Fortran convention of 1-based indices (rather 0-based indices).

133:       xs  = xs+1
134:       ys  = ys+1
135:       gxs = gxs+1
136:       gys = gys+1

138:       ye  = ys+ym-1
139:       xe  = xs+xm-1
140:       gye = gys+gym-1
141:       gxe = gxs+gxm-1

143: !  Set function evaluation routine and vector

145:       call DASetLocalFunction(da,FormFunctionLocal,ierr)
146:       call DASetLocalJacobian(da,FormJacobianLocal,ierr)
147: #if defined(PETSC_HAVE_ADIFOR)
148:       call DASetLocalAdiforFunction(da,                                             &
149:      &         g_FormFunctionLocal,ierr)
150: #endif
151:       call SNESSetFunction(snes,r,SNESDAFormFunction,da,ierr)

153: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
154: !  Create matrix data structure; set Jacobian evaluation routine
155: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

157: !  Set Jacobian matrix data structure and default Jacobian evaluation
158: !  routine. User can override with:
159: !     -snes_mf : matrix-free Newton-Krylov method with no preconditioning
160: !                (unless user explicitly sets preconditioner)
161: !     -snes_mf_operator : form preconditioning matrix as set by the user,
162: !                         but use matrix-free approx for Jacobian-vector
163: !                         products within Newton-Krylov method
164: !

166:       call DAGetMatrix(da,MATMPIAIJ,J,ierr)

168: #if defined(PETSC_HAVE_ADIFOR)
169:       call PetscOptionsGetLogical(PETSC_NULL_CHARACTER                            &
170:      &     ,'-adiformf_jacobian',                                                 &
171:      &     adiformf_jacobian,PETSC_NULL_INTEGER,ierr)
172:       if (adiformf_jacobian .eq. 1) then
173:         call DASetLocalAdiforMFFunction(da,                                       &
174:      &         m_FormFunctionLocal,ierr)
175:         call MatRegisterDAAD(ierr)
176:         call MatCreateDAAD(da,A,ierr)
177:         call MatDAADSetSNES(A,snes,ierr)
178:       else
179:         A = J
180:       endif
181: #else 
182:       A = J
183: #endif

185:       call SNESSetJacobian(snes,A,J,SNESDAComputeJacobian,                        &
186:      &                       da,ierr)

188: #if defined(PETSC_HAVE_ADIFOR)
189:       call PetscOptionsGetLogical(PETSC_NULL_CHARACTER                            &
190:      &     ,'-adifor_jacobian',                                                   &
191:      &     adifor_jacobian,PETSC_NULL_INTEGER,ierr)
192:       if (adifor_jacobian .eq. 1) then
193:         call SNESSetJacobian(snes,A,J,SNESDAComputeJacobianWithAdifor,            &
194:      &                         da,ierr)
195:       endif
196: #endif


199: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
200: !  Customize nonlinear solver; set runtime options
201: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

203: !  Set runtime options (e.g., -snes_monitor -snes_rtol <rtol> -ksp_type <type>)

205:           call SNESSetFromOptions(snes,ierr)

207: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
208: !  Evaluate initial guess; then solve nonlinear system.
209: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

211: !  Note: The user should initialize the vector, x, with the initial guess
212: !  for the nonlinear solver prior to calling SNESSolve().  In particular,
213: !  to employ an initial guess of zero, the user should explicitly set
214: !  this vector to zero by calling VecSet().

216:       call FormInitialGuess(x,ierr)
217:       call SNESSolve(snes,x,its,ierr)
218:       if (rank .eq. 0) then
219:          write(6,100) its
220:       endif
221:   100 format('Number of Newton iterations = ',i5)


224: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
225: !  Free work space.  All PETSc objects should be destroyed when they
226: !  are no longer needed.
227: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

229:       if (A .ne. J) call MatDestroy(A,ierr)
230:       call MatDestroy(J,ierr)
231:       call VecDestroy(x,ierr)
232:       call VecDestroy(r,ierr)
233:       call SNESDestroy(snes,ierr)
234:       call DADestroy(da,ierr)
235:       call PetscFinalize(ierr)
236:       end

238: ! ---------------------------------------------------------------------
239: !
240: !  FormInitialGuess - Forms initial approximation.
241: !
242: !  Input Parameters:
243: !  X - vector
244: !
245: !  Output Parameter:
246: !  X - vector
247: !
248: !  Notes:
249: !  This routine serves as a wrapper for the lower-level routine
250: !  "ApplicationInitialGuess", where the actual computations are
251: !  done using the standard Fortran style of treating the local
252: !  vector data as a multidimensional array over the local mesh.
253: !  This routine merely handles ghost point scatters and accesses
254: !  the local vector data via VecGetArray() and VecRestoreArray().
255: !
256:       subroutine FormInitialGuess(X,ierr)
257:       implicit none

259: #include "ex5f.h"

261: !  Input/output variables:
262:       Vec      X
263:       integer  ierr

265: !  Declarations for use with local arrays:
266:       PetscScalar lx_v(0:1)
267:       PetscOffset lx_i
268:       Vec         localX

270:       0

272: !  Get a pointer to vector data.
273: !    - For default PETSc vectors, VecGetArray() returns a pointer to
274: !      the data array.  Otherwise, the routine is implementation dependent.
275: !    - You MUST call VecRestoreArray() when you no longer need access to
276: !      the array.
277: !    - Note that the Fortran interface to VecGetArray() differs from the
278: !      C version.  See the users manual for details.

280:       call DAGetLocalVector(da,localX,ierr)
281:       call VecGetArray(localX,lx_v,lx_i,ierr)

283: !  Compute initial guess over the locally owned part of the grid

285:       call InitialGuessLocal(lx_v(lx_i),ierr)

287: !  Restore vector

289:       call VecRestoreArray(localX,lx_v,lx_i,ierr)

291: !  Insert values into global vector

293:       call DALocalToGlobal(da,localX,INSERT_VALUES,X,ierr)
294:       call DARestoreLocalVector(da,localX,ierr)
295:       return
296:       end

298: ! ---------------------------------------------------------------------
299: !
300: !  InitialGuessLocal - Computes initial approximation, called by
301: !  the higher level routine FormInitialGuess().
302: !
303: !  Input Parameter:
304: !  x - local vector data
305: !
306: !  Output Parameters:
307: !  x - local vector data
308: !  ierr - error code
309: !
310: !  Notes:
311: !  This routine uses standard Fortran-style computations over a 2-dim array.
312: !
313:       subroutine InitialGuessLocal(x,ierr)
314:       implicit none

316: #include "ex5f.h"

318: !  Input/output variables:
319:       PetscScalar  x(gxs:gxe,gys:gye)
320:       integer ierr

322: !  Local variables:
323:       integer  i,j,hxdhy,hydhx
324:       PetscScalar   temp1,temp,hx,hy,sc,one

326: !  Set parameters

328:       ierr   = 0
329:       one    = 1.0
330:       hx     = one/(dble(mx-1))
331:       hy     = one/(dble(my-1))
332:       sc     = hx*hy*lambda
333:       hxdhy  = hx/hy
334:       hydhx  = hy/hx
335:       temp1  = lambda/(lambda + one)

337:       do 20 j=ys,ye
338:          temp = dble(min(j-1,my-j))*hy
339:          do 10 i=xs,xe
340:             if (i .eq. 1 .or. j .eq. 1                                  &
341:      &             .or. i .eq. mx .or. j .eq. my) then
342:               x(i,j) = 0.0
343:             else
344:               x(i,j) = temp1 *                                          &
345:      &          sqrt(min(dble(min(i-1,mx-i)*hx),dble(temp)))
346:             endif
347:  10      continue
348:  20   continue

350:       return
351:       end

353: ! ---------------------------------------------------------------------
354: !
355: !  FormFunctionLocal - Computes nonlinear function, called by
356: !  the higher level routine FormFunction().
357: !
358: !  Input Parameter:
359: !  x - local vector data
360: !
361: !  Output Parameters:
362: !  f - local vector data, f(x)
363: !  ierr - error code
364: !
365: !  Notes:
366: !  This routine uses standard Fortran-style computations over a 2-dim array.
367: !
368: !     Process adifor: FormFunctionLocal
369: !
370:       subroutine FormFunctionLocal(info,x,f,dummy,ierr)

372:       implicit none

374: #include "ex5f.h"

376: !  Input/output variables:
377:       DALocalInfo info(DA_LOCAL_INFO_SIZE)
378:       PetscScalar x(gxs:gxe,gys:gye)
379:       PetscScalar f(xs:xe,ys:ye)
380:       integer     ierr
381:       PetscObject dummy

383: !  Local variables:
384:       PetscScalar   two,one,hx,hy,hxdhy,hydhx,sc
385:       PetscScalar   u,uxx,uyy
386:       integer  i,j


389:       xs     = info(DA_LOCAL_INFO_XS)+1
390:       xe     = xs+info(DA_LOCAL_INFO_XM)-1
391:       ys     = info(DA_LOCAL_INFO_YS)+1
392:       ye     = ys+info(DA_LOCAL_INFO_YM)-1
393:       mx     = info(DA_LOCAL_INFO_MX)
394:       my     = info(DA_LOCAL_INFO_MY)

396:       one    = 1.0
397:       two    = 2.0
398:       hx     = one/dble(mx-1)
399:       hy     = one/dble(my-1)
400:       sc     = hx*hy*lambda
401:       hxdhy  = hx/hy
402:       hydhx  = hy/hx

404: !  Compute function over the locally owned part of the grid

406:       do 20 j=ys,ye
407:          do 10 i=xs,xe
408:             if (i .eq. 1 .or. j .eq. 1                                  &
409:      &             .or. i .eq. mx .or. j .eq. my) then
410:                f(i,j) = x(i,j)
411:             else
412:                u = x(i,j)
413:                uxx = hydhx * (two*u                                     &
414:      &                - x(i-1,j) - x(i+1,j))
415:                uyy = hxdhy * (two*u - x(i,j-1) - x(i,j+1))
416:                f(i,j) = uxx + uyy - sc*exp(u)
417:             endif
418:  10      continue
419:  20   continue

421:       call PetscLogFlops(11*ym*xm,ierr)

423:       return
424:       end

426: ! ---------------------------------------------------------------------
427: !
428: !  FormJacobianLocal - Computes Jacobian matrix, called by
429: !  the higher level routine FormJacobian().
430: !
431: !  Input Parameters:
432: !  x        - local vector data
433: !
434: !  Output Parameters:
435: !  jac      - Jacobian matrix
436: !  jac_prec - optionally different preconditioning matrix (not used here)
437: !  ierr     - error code
438: !
439: !  Notes:
440: !  This routine uses standard Fortran-style computations over a 2-dim array.
441: !
442: !  Notes:
443: !  Due to grid point reordering with DAs, we must always work
444: !  with the local grid points, and then transform them to the new
445: !  global numbering with the "ltog" mapping (via DAGetGlobalIndices()).
446: !  We cannot work directly with the global numbers for the original
447: !  uniprocessor grid!
448: !
449: !  Two methods are available for imposing this transformation
450: !  when setting matrix entries:
451: !    (A) MatSetValuesLocal(), using the local ordering (including
452: !        ghost points!)
453: !        - Use DAGetGlobalIndices() to extract the local-to-global map
454: !        - Associate this map with the matrix by calling
455: !          MatSetLocalToGlobalMapping() once
456: !        - Set matrix entries using the local ordering
457: !          by calling MatSetValuesLocal()
458: !    (B) MatSetValues(), using the global ordering
459: !        - Use DAGetGlobalIndices() to extract the local-to-global map
460: !        - Then apply this map explicitly yourself
461: !        - Set matrix entries using the global ordering by calling
462: !          MatSetValues()
463: !  Option (A) seems cleaner/easier in many cases, and is the procedure
464: !  used in this example.
465: !
466:       subroutine FormJacobianLocal(info,x,jac,ctx,ierr)
467:       implicit none

469: #include "ex5f.h"

471: !  Input/output variables:
472:       PetscScalar x(gxs:gxe,gys:gye)
473:       Mat         jac
474:       integer     ierr,ctx
475:       DALocalInfo info(DA_LOCAL_INFO_SIZE)
476: 

478: !  Local variables:
479:       integer  row,col(5),i,j
480:       PetscScalar   two,one,hx,hy,hxdhy,hydhx,sc,v(5)

482: !  Set parameters

484:       one    = 1.0
485:       two    = 2.0
486:       hx     = one/dble(mx-1)
487:       hy     = one/dble(my-1)
488:       sc     = hx*hy
489:       hxdhy  = hx/hy
490:       hydhx  = hy/hx

492: !  Compute entries for the locally owned part of the Jacobian.
493: !   - Currently, all PETSc parallel matrix formats are partitioned by
494: !     contiguous chunks of rows across the processors.
495: !   - Each processor needs to insert only elements that it owns
496: !     locally (but any non-local elements will be sent to the
497: !     appropriate processor during matrix assembly).
498: !   - Here, we set all entries for a particular row at once.
499: !   - We can set matrix entries either using either
500: !     MatSetValuesLocal() or MatSetValues(), as discussed above.
501: !   - Note that MatSetValues() uses 0-based row and column numbers
502: !     in Fortran as well as in C.

504:       do 20 j=ys,ye
505:          row = (j - gys)*gxm + xs - gxs - 1
506:          do 10 i=xs,xe
507:             row = row + 1
508: !           boundary points
509:             if (i .eq. 1 .or. j .eq. 1                                  &
510:      &             .or. i .eq. mx .or. j .eq. my) then
511:                call MatSetValuesLocal(jac,1,row,1,row,one,              &
512:      &                           INSERT_VALUES,ierr)
513: !           interior grid points
514:             else
515:                v(1) = -hxdhy
516:                v(2) = -hydhx
517:                v(3) = two*(hydhx + hxdhy)                               &
518:      &                  - sc*lambda*exp(x(i,j))
519:                v(4) = -hydhx
520:                v(5) = -hxdhy
521:                col(1) = row - gxm
522:                col(2) = row - 1
523:                col(3) = row
524:                col(4) = row + 1
525:                col(5) = row + gxm
526:                call MatSetValuesLocal(jac,1,row,5,col,v,                &
527:      &                                INSERT_VALUES,ierr)
528:             endif
529:  10      continue
530:  20   continue
531:       call MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY,ierr)
532:       call MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY,ierr)
533:       return
534:       end