Actual source code: ex5f90.F90

  1: !
  2: !  Description: Solves a nonlinear system in parallel with SNES.
  3: !  We solve the  Bratu (SFI - solid fuel ignition) problem in a 2D rectangular
  4: !  domain, using distributed arrays (DMDAs) to partition the parallel grid.
  5: !  The command line options include:
  6: !    -par <parameter>, where <parameter> indicates the nonlinearity of the problem
  7: !       problem SFI:  <parameter> = Bratu parameter (0 <= par <= 6.81)
  8: !

 10: !
 11: !  --------------------------------------------------------------------------
 12: !
 13: !  Solid Fuel Ignition (SFI) problem.  This problem is modeled by
 14: !  the partial differential equation
 15: !
 16: !          -Laplacian u - lambda*exp(u) = 0,  0 < x,y < 1,
 17: !
 18: !  with boundary conditions
 19: !
 20: !           u = 0  for  x = 0, x = 1, y = 0, y = 1.
 21: !
 22: !  A finite difference approximation with the usual 5-point stencil
 23: !  is used to discretize the boundary value problem to obtain a nonlinear
 24: !  system of equations.
 25: !
 26: !  The uniprocessor version of this code is snes/tutorials/ex4f.F
 27: !
 28: !  --------------------------------------------------------------------------
 29: !  The following define must be used before including any PETSc include files
 30: !  into a module or interface. This is because they can't handle declarations
 31: !  in them
 32: !

 34:       module ex5f90module
 35: #include <petsc/finclude/petscsnes.h>
 36: #include <petsc/finclude/petscdmda.h>
 37:       use petscsnes
 38:       use petscdmda
 39:       type userctx
 40:         PetscInt xs,xe,xm,gxs,gxe,gxm
 41:         PetscInt ys,ye,ym,gys,gye,gym
 42:         PetscInt mx,my
 43:         PetscMPIInt rank
 44:         PetscReal lambda
 45:       end type userctx

 47:       contains
 48: ! ---------------------------------------------------------------------
 49: !
 50: !  FormFunction - Evaluates nonlinear function, F(x).
 51: !
 52: !  Input Parameters:
 53: !  snes - the SNES context
 54: !  X - input vector
 55: !  dummy - optional user-defined context, as set by SNESSetFunction()
 56: !          (not used here)
 57: !
 58: !  Output Parameter:
 59: !  F - function vector
 60: !
 61: !  Notes:
 62: !  This routine serves as a wrapper for the lower-level routine
 63: !  "FormFunctionLocal", where the actual computations are
 64: !  done using the standard Fortran style of treating the local
 65: !  vector data as a multidimensional array over the local mesh.
 66: !  This routine merely handles ghost point scatters and accesses
 67: !  the local vector data via VecGetArray() and VecRestoreArray().
 68: !
 69:       subroutine FormFunction(snes,X,F,user,ierr)
 70:       implicit none

 72: !  Input/output variables:
 73:       SNES           snes
 74:       Vec            X,F
 75:       PetscErrorCode ierr
 76:       type (userctx) user
 77:       DM             da

 79: !  Declarations for use with local arrays:
 80:       PetscScalar,pointer :: lx_v(:),lf_v(:)
 81:       Vec            localX

 83: !  Scatter ghost points to local vector, using the 2-step process
 84: !     DMGlobalToLocalBegin(), DMGlobalToLocalEnd().
 85: !  By placing code between these two statements, computations can
 86: !  be done while messages are in transition.
 87:       PetscCall(SNESGetDM(snes,da,ierr))
 88:       PetscCall(DMGetLocalVector(da,localX,ierr))
 89:       PetscCall(DMGlobalToLocalBegin(da,X,INSERT_VALUES,localX,ierr))
 90:       PetscCall(DMGlobalToLocalEnd(da,X,INSERT_VALUES,localX,ierr))

 92: !  Get a pointer to vector data.
 93: !    - For default PETSc vectors, VecGetArray() returns a pointer to
 94: !      the data array. Otherwise, the routine is implementation dependent.
 95: !    - You MUST call VecRestoreArray() when you no longer need access to
 96: !      the array.
 97: !    - Note that the interface to VecGetArray() differs from VecGetArray().

 99:       PetscCall(VecGetArray(localX,lx_v,ierr))
100:       PetscCall(VecGetArray(F,lf_v,ierr))

102: !  Compute function over the locally owned part of the grid
103:       PetscCall(FormFunctionLocal(lx_v,lf_v,user,ierr))

105: !  Restore vectors
106:       PetscCall(VecRestoreArray(localX,lx_v,ierr))
107:       PetscCall(VecRestoreArray(F,lf_v,ierr))

109: !  Insert values into global vector

111:       PetscCall(DMRestoreLocalVector(da,localX,ierr))
112:       PetscCall(PetscLogFlops(11.0d0*user%ym*user%xm,ierr))

114: !      PetscCallA(VecView(X,PETSC_VIEWER_STDOUT_WORLD,ierr))
115: !      PetscCallA(VecView(F,PETSC_VIEWER_STDOUT_WORLD,ierr))
116:       end subroutine formfunction
117:       end module ex5f90module

119:       module ex5f90moduleinterfaces
120:         use ex5f90module

122:       Interface SNESSetApplicationContext
123:         Subroutine SNESSetApplicationContext(snes,ctx,ierr)
124:         use ex5f90module
125:           SNES snes
126:           type(userctx) ctx
127:           PetscErrorCode ierr
128:         End Subroutine
129:       End Interface SNESSetApplicationContext

131:       Interface SNESGetApplicationContext
132:         Subroutine SNESGetApplicationContext(snes,ctx,ierr)
133:         use ex5f90module
134:           SNES snes
135:           type(userctx), pointer :: ctx
136:           PetscErrorCode ierr
137:         End Subroutine
138:       End Interface SNESGetApplicationContext
139:       end module ex5f90moduleinterfaces

141:       program main
142:       use ex5f90module
143:       use ex5f90moduleinterfaces
144:       implicit none
145: !

147: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
148: !                   Variable declarations
149: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
150: !
151: !  Variables:
152: !     snes        - nonlinear solver
153: !     x, r        - solution, residual vectors
154: !     J           - Jacobian matrix
155: !     its         - iterations for convergence
156: !     Nx, Ny      - number of preocessors in x- and y- directions
157: !     matrix_free - flag - 1 indicates matrix-free version
158: !
159:       SNES             snes
160:       Vec              x,r
161:       Mat              J
162:       PetscErrorCode   ierr
163:       PetscInt         its
164:       PetscBool        flg,matrix_free
165:       PetscInt         ione,nfour
166:       PetscReal lambda_max,lambda_min
167:       type (userctx)   user
168:       DM               da

170: !  Note: Any user-defined Fortran routines (such as FormJacobian)
171: !  MUST be declared as external.
172:       external FormInitialGuess,FormJacobian

174: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
175: !  Initialize program
176: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
177:       PetscCallA(PetscInitialize(ierr))
178:       PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD,user%rank,ierr))

180: !  Initialize problem parameters
181:       lambda_max  = 6.81
182:       lambda_min  = 0.0
183:       user%lambda = 6.0
184:       ione = 1
185:       nfour = 4
186:       PetscCallA(PetscOptionsGetReal(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-par',user%lambda,flg,ierr))
187:       PetscCheckA(user%lambda .lt. lambda_max .and. user%lambda .gt. lambda_min,PETSC_COMM_SELF,PETSC_ERR_USER,'Lambda provided with -par is out of range')

189: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
190: !  Create nonlinear solver context
191: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
192:       PetscCallA(SNESCreate(PETSC_COMM_WORLD,snes,ierr))

194: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
195: !  Create vector data structures; set function evaluation routine
196: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

198: !  Create distributed array (DMDA) to manage parallel grid and vectors

200: ! This really needs only the star-type stencil, but we use the box
201: ! stencil temporarily.
202:       PetscCallA(DMDACreate2d(PETSC_COMM_WORLD,DM_BOUNDARY_NONE,DM_BOUNDARY_NONE,DMDA_STENCIL_BOX,nfour,nfour,PETSC_DECIDE,PETSC_DECIDE,ione,ione,PETSC_NULL_INTEGER_ARRAY,PETSC_NULL_INTEGER_ARRAY,da,ierr))
203:       PetscCallA(DMSetFromOptions(da,ierr))
204:       PetscCallA(DMSetUp(da,ierr))

206:       PetscCallA(DMDAGetInfo(da,PETSC_NULL_INTEGER,user%mx,user%my,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_INTEGER,PETSC_NULL_DMBOUNDARYTYPE,PETSC_NULL_DMBOUNDARYTYPE,PETSC_NULL_DMBOUNDARYTYPE,PETSC_NULL_DMDASTENCILTYPE,ierr))

208: !
209: !   Visualize the distribution of the array across the processors
210: !
211: !     PetscCallA(DMView(da,PETSC_VIEWER_DRAW_WORLD,ierr))

213: !  Extract global and local vectors from DMDA; then duplicate for remaining
214: !  vectors that are the same types
215:       PetscCallA(DMCreateGlobalVector(da,x,ierr))
216:       PetscCallA(VecDuplicate(x,r,ierr))

218: !  Get local grid boundaries (for 2-dimensional DMDA)
219:       PetscCallA(DMDAGetCorners(da,user%xs,user%ys,PETSC_NULL_INTEGER,user%xm,user%ym,PETSC_NULL_INTEGER,ierr))
220:       PetscCallA(DMDAGetGhostCorners(da,user%gxs,user%gys,PETSC_NULL_INTEGER,user%gxm,user%gym,PETSC_NULL_INTEGER,ierr))

222: !  Here we shift the starting indices up by one so that we can easily
223: !  use the Fortran convention of 1-based indices (rather 0-based indices).
224:       user%xs  = user%xs+1
225:       user%ys  = user%ys+1
226:       user%gxs = user%gxs+1
227:       user%gys = user%gys+1

229:       user%ye  = user%ys+user%ym-1
230:       user%xe  = user%xs+user%xm-1
231:       user%gye = user%gys+user%gym-1
232:       user%gxe = user%gxs+user%gxm-1

234:       PetscCallA(SNESSetApplicationContext(snes,user,ierr))

236: !  Set function evaluation routine and vector
237:       PetscCallA(SNESSetFunction(snes,r,FormFunction,user,ierr))

239: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
240: !  Create matrix data structure; set Jacobian evaluation routine
241: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

243: !  Set Jacobian matrix data structure and default Jacobian evaluation
244: !  routine. User can override with:
245: !     -snes_fd : default finite differencing approximation of Jacobian
246: !     -snes_mf : matrix-free Newton-Krylov method with no preconditioning
247: !                (unless user explicitly sets preconditioner)
248: !     -snes_mf_operator : form preconditioning matrix as set by the user,
249: !                         but use matrix-free approx for Jacobian-vector
250: !                         products within Newton-Krylov method
251: !
252: !  Note:  For the parallel case, vectors and matrices MUST be partitioned
253: !     accordingly.  When using distributed arrays (DMDAs) to create vectors,
254: !     the DMDAs determine the problem partitioning.  We must explicitly
255: !     specify the local matrix dimensions upon its creation for compatibility
256: !     with the vector distribution.  Thus, the generic MatCreate() routine
257: !     is NOT sufficient when working with distributed arrays.
258: !
259: !     Note: Here we only approximately preallocate storage space for the
260: !     Jacobian.  See the users manual for a discussion of better techniques
261: !     for preallocating matrix memory.

263:       PetscCallA(PetscOptionsHasName(PETSC_NULL_OPTIONS,PETSC_NULL_CHARACTER,'-snes_mf',matrix_free,ierr))
264:       if (.not. matrix_free) then
265:         PetscCallA(DMSetMatType(da,MATAIJ,ierr))
266:         PetscCallA(DMCreateMatrix(da,J,ierr))
267:         PetscCallA(SNESSetJacobian(snes,J,J,FormJacobian,user,ierr))
268:       endif

270: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
271: !  Customize nonlinear solver; set runtime options
272: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
273: !  Set runtime options (e.g., -snes_monitor -snes_rtol <rtol> -ksp_type <type>)
274:       PetscCallA(SNESSetDM(snes,da,ierr))
275:       PetscCallA(SNESSetFromOptions(snes,ierr))

277: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
278: !  Evaluate initial guess; then solve nonlinear system.
279: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
280: !  Note: The user should initialize the vector, x, with the initial guess
281: !  for the nonlinear solver prior to calling SNESSolve().  In particular,
282: !  to employ an initial guess of zero, the user should explicitly set
283: !  this vector to zero by calling VecSet().

285:       PetscCallA(FormInitialGuess(snes,x,ierr))
286:       PetscCallA(SNESSolve(snes,PETSC_NULL_VEC,x,ierr))
287:       PetscCallA(SNESGetIterationNumber(snes,its,ierr))
288:       if (user%rank .eq. 0) then
289:          write(6,100) its
290:       endif
291:   100 format('Number of SNES iterations = ',i5)

293: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
294: !  Free work space.  All PETSc objects should be destroyed when they
295: !  are no longer needed.
296: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
297:       if (.not. matrix_free) PetscCallA(MatDestroy(J,ierr))
298:       PetscCallA(VecDestroy(x,ierr))
299:       PetscCallA(VecDestroy(r,ierr))
300:       PetscCallA(SNESDestroy(snes,ierr))
301:       PetscCallA(DMDestroy(da,ierr))

303:       PetscCallA(PetscFinalize(ierr))
304:       end

306: ! ---------------------------------------------------------------------
307: !
308: !  FormInitialGuess - Forms initial approximation.
309: !
310: !  Input Parameters:
311: !  X - vector
312: !
313: !  Output Parameter:
314: !  X - vector
315: !
316: !  Notes:
317: !  This routine serves as a wrapper for the lower-level routine
318: !  "InitialGuessLocal", where the actual computations are
319: !  done using the standard Fortran style of treating the local
320: !  vector data as a multidimensional array over the local mesh.
321: !  This routine merely handles ghost point scatters and accesses
322: !  the local vector data via VecGetArray() and VecRestoreArray().
323: !
324:       subroutine FormInitialGuess(snes,X,ierr)
325:       use ex5f90module
326:       use ex5f90moduleinterfaces
327:       implicit none

329: !  Input/output variables:
330:       SNES           snes
331:       type(userctx), pointer:: puser
332:       Vec            X
333:       PetscErrorCode ierr
334:       DM             da

336: !  Declarations for use with local arrays:
337:       PetscScalar,pointer :: lx_v(:)

339:       ierr = 0
340:       PetscCallA(SNESGetDM(snes,da,ierr))
341:       PetscCallA(SNESGetApplicationContext(snes,puser,ierr))
342: !  Get a pointer to vector data.
343: !    - For default PETSc vectors, VecGetArray() returns a pointer to
344: !      the data array. Otherwise, the routine is implementation dependent.
345: !    - You MUST call VecRestoreArray() when you no longer need access to
346: !      the array.
347: !    - Note that the interface to VecGetArray() differs from VecGetArray().

349:       PetscCallA(VecGetArray(X,lx_v,ierr))

351: !  Compute initial guess over the locally owned part of the grid
352:       PetscCallA(InitialGuessLocal(puser,lx_v,ierr))

354: !  Restore vector
355:       PetscCallA(VecRestoreArray(X,lx_v,ierr))

357: !  Insert values into global vector

359:       end

361: ! ---------------------------------------------------------------------
362: !
363: !  InitialGuessLocal - Computes initial approximation, called by
364: !  the higher level routine FormInitialGuess().
365: !
366: !  Input Parameter:
367: !  x - local vector data
368: !
369: !  Output Parameters:
370: !  x - local vector data
371: !  ierr - error code
372: !
373: !  Notes:
374: !  This routine uses standard Fortran-style computations over a 2-dim array.
375: !
376:       subroutine InitialGuessLocal(user,x,ierr)
377:       use ex5f90module
378:       implicit none

380: !  Input/output variables:
381:       type (userctx)         user
382:       PetscScalar  x(user%xs:user%xe,user%ys:user%ye)
383:       PetscErrorCode ierr

385: !  Local variables:
386:       PetscInt  i,j
387:       PetscReal   temp1,temp,hx,hy
388:       PetscReal   one

390: !  Set parameters

392:       ierr   = 0
393:       one    = 1.0
394:       hx     = one/(user%mx-1)
395:       hy     = one/(user%my-1)
396:       temp1  = user%lambda/(user%lambda + one)

398:       do 20 j=user%ys,user%ye
399:          temp = min(j-1,user%my-j)*hy
400:          do 10 i=user%xs,user%xe
401:             if (i .eq. 1 .or. j .eq. 1 .or. i .eq. user%mx .or. j .eq. user%my) then
402:               x(i,j) = 0.0
403:             else
404:               x(i,j) = temp1 * sqrt(min(hx*min(i-1,user%mx-i),temp))
405:             endif
406:  10      continue
407:  20   continue

409:       end

411: ! ---------------------------------------------------------------------
412: !
413: !  FormFunctionLocal - Computes nonlinear function, called by
414: !  the higher level routine FormFunction().
415: !
416: !  Input Parameter:
417: !  x - local vector data
418: !
419: !  Output Parameters:
420: !  f - local vector data, f(x)
421: !  ierr - error code
422: !
423: !  Notes:
424: !  This routine uses standard Fortran-style computations over a 2-dim array.
425: !
426:       subroutine FormFunctionLocal(x,f,user,ierr)
427:       use ex5f90module

429:       implicit none

431: !  Input/output variables:
432:       type (userctx) user
433:       PetscScalar  x(user%gxs:user%gxe,user%gys:user%gye)
434:       PetscScalar  f(user%xs:user%xe,user%ys:user%ye)
435:       PetscErrorCode ierr

437: !  Local variables:
438:       PetscScalar two,one,hx,hy,hxdhy,hydhx,sc
439:       PetscScalar u,uxx,uyy
440:       PetscInt  i,j

442:       one    = 1.0
443:       two    = 2.0
444:       hx     = one/(user%mx-1)
445:       hy     = one/(user%my-1)
446:       sc     = hx*hy*user%lambda
447:       hxdhy  = hx/hy
448:       hydhx  = hy/hx

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

452:       do 20 j=user%ys,user%ye
453:          do 10 i=user%xs,user%xe
454:             if (i .eq. 1 .or. j .eq. 1 .or. i .eq. user%mx .or. j .eq. user%my) then
455:                f(i,j) = x(i,j)
456:             else
457:                u = x(i,j)
458:                uxx = hydhx * (two*u - x(i-1,j) - x(i+1,j))
459:                uyy = hxdhy * (two*u - x(i,j-1) - x(i,j+1))
460:                f(i,j) = uxx + uyy - sc*exp(u)
461:             endif
462:  10      continue
463:  20   continue

465:       end

467: ! ---------------------------------------------------------------------
468: !
469: !  FormJacobian - Evaluates Jacobian matrix.
470: !
471: !  Input Parameters:
472: !  snes     - the SNES context
473: !  x        - input vector
474: !  dummy    - optional user-defined context, as set by SNESSetJacobian()
475: !             (not used here)
476: !
477: !  Output Parameters:
478: !  jac      - Jacobian matrix
479: !  jac_prec - optionally different preconditioning matrix (not used here)
480: !
481: !  Notes:
482: !  This routine serves as a wrapper for the lower-level routine
483: !  "FormJacobianLocal", where the actual computations are
484: !  done using the standard Fortran style of treating the local
485: !  vector data as a multidimensional array over the local mesh.
486: !  This routine merely accesses the local vector data via
487: !  VecGetArray() and VecRestoreArray().
488: !
489: !  Notes:
490: !  Due to grid point reordering with DMDAs, we must always work
491: !  with the local grid points, and then transform them to the new
492: !  global numbering with the "ltog" mapping
493: !  We cannot work directly with the global numbers for the original
494: !  uniprocessor grid!
495: !
496: !  Two methods are available for imposing this transformation
497: !  when setting matrix entries:
498: !    (A) MatSetValuesLocal(), using the local ordering (including
499: !        ghost points!)
500: !        - Set matrix entries using the local ordering
501: !          by calling MatSetValuesLocal()
502: !    (B) MatSetValues(), using the global ordering

504: !        - Set matrix entries using the global ordering by calling
505: !          MatSetValues()
506: !  Option (A) seems cleaner/easier in many cases, and is the procedure
507: !  used in this example.
508: !
509:       subroutine FormJacobian(snes,X,jac,jac_prec,user,ierr)
510:       use ex5f90module
511:       implicit none

513: !  Input/output variables:
514:       SNES         snes
515:       Vec          X
516:       Mat          jac,jac_prec
517:       type(userctx)  user
518:       PetscErrorCode ierr
519:       DM             da

521: !  Declarations for use with local arrays:
522:       PetscScalar,pointer :: lx_v(:)
523:       Vec            localX

525: !  Scatter ghost points to local vector, using the 2-step process
526: !     DMGlobalToLocalBegin(), DMGlobalToLocalEnd()
527: !  Computations can be done while messages are in transition,
528: !  by placing code between these two statements.

530:       PetscCallA(SNESGetDM(snes,da,ierr))
531:       PetscCallA(DMGetLocalVector(da,localX,ierr))
532:       PetscCallA(DMGlobalToLocalBegin(da,X,INSERT_VALUES,localX,ierr))
533:       PetscCallA(DMGlobalToLocalEnd(da,X,INSERT_VALUES,localX,ierr))

535: !  Get a pointer to vector data
536:       PetscCallA(VecGetArray(localX,lx_v,ierr))

538: !  Compute entries for the locally owned part of the Jacobian preconditioner.
539:       PetscCallA(FormJacobianLocal(lx_v,jac_prec,user,ierr))

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

546:       PetscCallA(MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY,ierr))
547:       if (jac .ne. jac_prec) then
548:          PetscCallA(MatAssemblyBegin(jac_prec,MAT_FINAL_ASSEMBLY,ierr))
549:       endif
550:       PetscCallA(VecRestoreArray(localX,lx_v,ierr))
551:       PetscCallA(DMRestoreLocalVector(da,localX,ierr))
552:       PetscCallA(MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY,ierr))
553:       if (jac .ne. jac_prec) then
554:         PetscCallA(MatAssemblyEnd(jac_prec,MAT_FINAL_ASSEMBLY,ierr))
555:       endif

557: !  Tell the matrix we will never add a new nonzero location to the
558: !  matrix. If we do it will generate an error.

560:       PetscCallA(MatSetOption(jac,MAT_NEW_NONZERO_LOCATION_ERR,PETSC_TRUE,ierr))

562:       end

564: ! ---------------------------------------------------------------------
565: !
566: !  FormJacobianLocal - Computes Jacobian preconditioner matrix,
567: !  called by the higher level routine FormJacobian().
568: !
569: !  Input Parameters:
570: !  x        - local vector data
571: !
572: !  Output Parameters:
573: !  jac_prec - Jacobian preconditioner matrix
574: !  ierr     - error code
575: !
576: !  Notes:
577: !  This routine uses standard Fortran-style computations over a 2-dim array.
578: !
579: !  Notes:
580: !  Due to grid point reordering with DMDAs, we must always work
581: !  with the local grid points, and then transform them to the new
582: !  global numbering with the "ltog" mapping
583: !  We cannot work directly with the global numbers for the original
584: !  uniprocessor grid!
585: !
586: !  Two methods are available for imposing this transformation
587: !  when setting matrix entries:
588: !    (A) MatSetValuesLocal(), using the local ordering (including
589: !        ghost points!)
590: !        - Set matrix entries using the local ordering
591: !          by calling MatSetValuesLocal()
592: !    (B) MatSetValues(), using the global ordering
593: !        - Then apply this map explicitly yourself
594: !        - Set matrix entries using the global ordering by calling
595: !          MatSetValues()
596: !  Option (A) seems cleaner/easier in many cases, and is the procedure
597: !  used in this example.
598: !
599:       subroutine FormJacobianLocal(x,jac_prec,user,ierr)
600:       use ex5f90module
601:       implicit none

603: !  Input/output variables:
604:       type (userctx) user
605:       PetscScalar    x(user%gxs:user%gxe,user%gys:user%gye)
606:       Mat            jac_prec
607:       PetscErrorCode ierr

609: !  Local variables:
610:       PetscInt    row,col(5),i,j
611:       PetscInt    ione,ifive
612:       PetscScalar two,one,hx,hy,hxdhy
613:       PetscScalar hydhx,sc,v(5)

615: !  Set parameters
616:       ione   = 1
617:       ifive  = 5
618:       one    = 1.0
619:       two    = 2.0
620:       hx     = one/(user%mx-1)
621:       hy     = one/(user%my-1)
622:       sc     = hx*hy
623:       hxdhy  = hx/hy
624:       hydhx  = hy/hx

626: !  Compute entries for the locally owned part of the Jacobian.
627: !   - Currently, all PETSc parallel matrix formats are partitioned by
628: !     contiguous chunks of rows across the processors.
629: !   - Each processor needs to insert only elements that it owns
630: !     locally (but any non-local elements will be sent to the
631: !     appropriate processor during matrix assembly).
632: !   - Here, we set all entries for a particular row at once.
633: !   - We can set matrix entries either using either
634: !     MatSetValuesLocal() or MatSetValues(), as discussed above.
635: !   - Note that MatSetValues() uses 0-based row and column numbers
636: !     in Fortran as well as in C.

638:       do 20 j=user%ys,user%ye
639:          row = (j - user%gys)*user%gxm + user%xs - user%gxs - 1
640:          do 10 i=user%xs,user%xe
641:             row = row + 1
642: !           boundary points
643:             if (i .eq. 1 .or. j .eq. 1 .or. i .eq. user%mx .or. j .eq. user%my) then
644:                col(1) = row
645:                v(1)   = one
646:                PetscCallA(MatSetValuesLocal(jac_prec,ione,[row],ione,col,v,INSERT_VALUES,ierr))
647: !           interior grid points
648:             else
649:                v(1) = -hxdhy
650:                v(2) = -hydhx
651:                v(3) = two*(hydhx + hxdhy) - sc*user%lambda*exp(x(i,j))
652:                v(4) = -hydhx
653:                v(5) = -hxdhy
654:                col(1) = row - user%gxm
655:                col(2) = row - 1
656:                col(3) = row
657:                col(4) = row + 1
658:                col(5) = row + user%gxm
659:                PetscCallA(MatSetValuesLocal(jac_prec,ione,[row],ifive,col,v,INSERT_VALUES,ierr))
660:             endif
661:  10      continue
662:  20   continue

664:       end

666: !
667: !/*TEST
668: !
669: !   test:
670: !      nsize: 4
671: !      args: -snes_mf -pc_type none -da_processors_x 4 -da_processors_y 1 -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always
672: !      requires: !single
673: !
674: !   test:
675: !      suffix: 2
676: !      nsize: 4
677: !      args: -da_processors_x 2 -da_processors_y 2 -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always
678: !      requires: !single
679: !
680: !   test:
681: !      suffix: 3
682: !      nsize: 3
683: !      args: -snes_fd -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always
684: !      requires: !single
685: !
686: !   test:
687: !      suffix: 4
688: !      nsize: 3
689: !      args: -snes_mf_operator -snes_monitor_short -ksp_gmres_cgs_refinement_type refine_always
690: !      requires: !single
691: !
692: !   test:
693: !      suffix: 5
694: !      requires: !single
695: !
696: !TEST*/