Actual source code: ex1f.F

petsc-3.5.1 2014-07-31
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  1: !
  2: !
  3: !  Description: Uses the Newton method to solve a two-variable system.
  4: !
  5: !/*T
  6: !  Concepts: SNES^basic uniprocessor example
  7: !  Processors: 1
  8: !T*/
  9: !
 10: ! -----------------------------------------------------------------------

 12:       program main
 13:       implicit none

 15: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 16: !                    Include files
 17: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 18: !
 19: !  The following include statements are generally used in SNES Fortran
 20: !  programs:
 21: !     petscsys.h       - base PETSc routines
 22: !     petscvec.h    - vectors
 23: !     petscmat.h    - matrices
 24: !     petscksp.h    - Krylov subspace methods
 25: !     petscpc.h     - preconditioners
 26: !     petscsnes.h   - SNES interface
 27: !  Other include statements may be needed if using additional PETSc
 28: !  routines in a Fortran program, e.g.,
 29: !     petscviewer.h - viewers
 30: !     petscis.h     - index sets
 31: !
 32: #include <finclude/petscsys.h>
 33: #include <finclude/petscvec.h>
 34: #include <finclude/petscmat.h>
 35: #include <finclude/petscksp.h>
 36: #include <finclude/petscpc.h>
 37: #include <finclude/petscsnes.h>
 38: !
 39: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 40: !                   Variable declarations
 41: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 42: !
 43: !  Variables:
 44: !     snes        - nonlinear solver
 45: !     ksp        - linear solver
 46: !     pc          - preconditioner context
 47: !     ksp         - Krylov subspace method context
 48: !     x, r        - solution, residual vectors
 49: !     J           - Jacobian matrix
 50: !     its         - iterations for convergence
 51: !
 52:       SNES     snes
 53:       PC       pc
 54:       KSP      ksp
 55:       Vec      x,r
 56:       Mat      J
 57:       SNESLineSearch linesearch
 58:       PetscErrorCode  ierr
 59:       PetscInt its,i2,i20
 60:       PetscMPIInt size,rank
 61:       PetscScalar   pfive
 62:       PetscReal   tol
 63:       PetscBool   setls

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

 68:       external FormFunction, FormJacobian, MyLineSearch

 70: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 71: !                   Macro definitions
 72: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 73: !
 74: !  Macros to make clearer the process of setting values in vectors and
 75: !  getting values from vectors.  These vectors are used in the routines
 76: !  FormFunction() and FormJacobian().
 77: !   - The element lx_a(ib) is element ib in the vector x
 78: !
 79: #define lx_a(ib) lx_v(lx_i + (ib))
 80: #define lf_a(ib) lf_v(lf_i + (ib))
 81: !
 82: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 83: !                 Beginning of program
 84: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

 86:       call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
 87:       call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
 88:       call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
 89:       if (size .ne. 1) then
 90:          if (rank .eq. 0) then
 91:             write(6,*) 'This is a uniprocessor example only!'
 92:          endif
 93:          SETERRQ(PETSC_COMM_SELF,1,' ',ierr)
 94:       endif

 96:       i2  = 2
 97:       i20 = 20
 98: ! - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - -
 99: !  Create nonlinear solver context
100: ! - - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - -

102:       call SNESCreate(PETSC_COMM_WORLD,snes,ierr)

104: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
105: !  Create matrix and vector data structures; set corresponding routines
106: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

108: !  Create vectors for solution and nonlinear function

110:       call VecCreateSeq(PETSC_COMM_SELF,i2,x,ierr)
111:       call VecDuplicate(x,r,ierr)

113: !  Create Jacobian matrix data structure

115:       call MatCreate(PETSC_COMM_SELF,J,ierr)
116:       call MatSetSizes(J,PETSC_DECIDE,PETSC_DECIDE,i2,i2,ierr)
117:       call MatSetFromOptions(J,ierr)
118:       call MatSetUp(J,ierr)

120: !  Set function evaluation routine and vector

122:       call SNESSetFunction(snes,r,FormFunction,PETSC_NULL_OBJECT,ierr)

124: !  Set Jacobian matrix data structure and Jacobian evaluation routine

126:       call SNESSetJacobian(snes,J,J,FormJacobian,PETSC_NULL_OBJECT,     &
127:      &     ierr)

129: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
130: !  Customize nonlinear solver; set runtime options
131: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

133: !  Set linear solver defaults for this problem. By extracting the
134: !  KSP, KSP, and PC contexts from the SNES context, we can then
135: !  directly call any KSP, KSP, and PC routines to set various options.

137:       call SNESGetKSP(snes,ksp,ierr)
138:       call KSPGetPC(ksp,pc,ierr)
139:       call PCSetType(pc,PCNONE,ierr)
140:       tol = 1.e-4
141:       call KSPSetTolerances(ksp,tol,PETSC_DEFAULT_REAL,                  &
142:      &                      PETSC_DEFAULT_REAL,i20,ierr)

144: !  Set SNES/KSP/KSP/PC runtime options, e.g.,
145: !      -snes_view -snes_monitor -ksp_type <ksp> -pc_type <pc>
146: !  These options will override those specified above as long as
147: !  SNESSetFromOptions() is called _after_ any other customization
148: !  routines.


151:       call SNESSetFromOptions(snes,ierr)

153:       call PetscOptionsHasName(PETSC_NULL_CHARACTER,'-setls',setls,ierr)

155:       if (setls) then
156:         call SNESGetLineSearch(snes, linesearch, ierr)
157:         call SNESLineSearchSetType(linesearch, "shell", ierr)
158:         call SNESLineSearchShellSetUserFunc(linesearch, MyLineSearch,   &
159:      &PETSC_NULL_OBJECT, ierr)
160:       endif

162: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
163: !  Evaluate initial guess; then solve nonlinear system
164: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

171:       pfive = 0.5
172:       call VecSet(x,pfive,ierr)
173:       call SNESSolve(snes,PETSC_NULL_OBJECT,x,ierr)
174:       call SNESGetIterationNumber(snes,its,ierr);
175:       if (rank .eq. 0) then
176:          write(6,100) its
177:       endif
178:   100 format('Number of SNES iterations = ',i5)

180: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
181: !  Free work space.  All PETSc objects should be destroyed when they
182: !  are no longer needed.
183: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

185:       call VecDestroy(x,ierr)
186:       call VecDestroy(r,ierr)
187:       call MatDestroy(J,ierr)
188:       call SNESDestroy(snes,ierr)
189:       call PetscFinalize(ierr)
190:       end
191: !
192: ! ------------------------------------------------------------------------
193: !
194: !  FormFunction - Evaluates nonlinear function, F(x).
195: !
196: !  Input Parameters:
197: !  snes - the SNES context
198: !  x - input vector
199: !  dummy - optional user-defined context (not used here)
200: !
201: !  Output Parameter:
202: !  f - function vector
203: !
204:       subroutine FormFunction(snes,x,f,dummy,ierr)
205:       implicit none

207: #include <finclude/petscsys.h>
208: #include <finclude/petscvec.h>
209: #include <finclude/petscsnes.h>

211:       SNES     snes
212:       Vec      x,f
213:       PetscErrorCode ierr
214:       integer dummy(*)

216: !  Declarations for use with local arrays

218:       PetscScalar  lx_v(1),lf_v(1)
219:       PetscOffset  lx_i,lf_i

221: !  Get pointers to vector data.
222: !    - For default PETSc vectors, VecGetArray() returns a pointer to
223: !      the data array.  Otherwise, the routine is implementation dependent.
224: !    - You MUST call VecRestoreArray() when you no longer need access to
225: !      the array.
226: !    - Note that the Fortran interface to VecGetArray() differs from the
227: !      C version.  See the Fortran chapter of the users manual for details.

229:       call VecGetArray(x,lx_v,lx_i,ierr)
230:       call VecGetArray(f,lf_v,lf_i,ierr)

232: !  Compute function

234:       lf_a(1) = lx_a(1)*lx_a(1)                                         &
235:      &          + lx_a(1)*lx_a(2) - 3.0
236:       lf_a(2) = lx_a(1)*lx_a(2)                                         &
237:      &          + lx_a(2)*lx_a(2) - 6.0

239: !  Restore vectors

241:       call VecRestoreArray(x,lx_v,lx_i,ierr)
242:       call VecRestoreArray(f,lf_v,lf_i,ierr)

244:       return
245:       end

247: ! ---------------------------------------------------------------------
248: !
249: !  FormJacobian - Evaluates Jacobian matrix.
250: !
251: !  Input Parameters:
252: !  snes - the SNES context
253: !  x - input vector
254: !  dummy - optional user-defined context (not used here)
255: !
256: !  Output Parameters:
257: !  A - Jacobian matrix
258: !  B - optionally different preconditioning matrix
259: !  flag - flag indicating matrix structure
260: !
261:       subroutine FormJacobian(snes,X,jac,B,dummy,ierr)
262:       implicit none

264: #include <finclude/petscsys.h>
265: #include <finclude/petscvec.h>
266: #include <finclude/petscmat.h>
267: #include <finclude/petscpc.h>
268: #include <finclude/petscsnes.h>

270:       SNES         snes
271:       Vec          X
272:       Mat          jac,B
273:       PetscScalar  A(4)
274:       PetscErrorCode ierr
275:       PetscInt idx(2),i2
276:       integer dummy(*)

278: !  Declarations for use with local arrays

280:       PetscScalar lx_v(1)
281:       PetscOffset lx_i

283: !  Get pointer to vector data

285:       i2 = 2
286:       call VecGetArray(x,lx_v,lx_i,ierr)

288: !  Compute Jacobian entries and insert into matrix.
289: !   - Since this is such a small problem, we set all entries for
290: !     the matrix at once.
291: !   - Note that MatSetValues() uses 0-based row and column numbers
292: !     in Fortran as well as in C (as set here in the array idx).

294:       idx(1) = 0
295:       idx(2) = 1
296:       A(1) = 2.0*lx_a(1) + lx_a(2)
297:       A(2) = lx_a(1)
298:       A(3) = lx_a(2)
299:       A(4) = lx_a(1) + 2.0*lx_a(2)
300:       call MatSetValues(jac,i2,idx,i2,idx,A,INSERT_VALUES,ierr)

302: !  Restore vector

304:       call VecRestoreArray(x,lx_v,lx_i,ierr)

306: !  Assemble matrix

308:       call MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY,ierr)
309:       call MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY,ierr)

311:       return
312:       end


315:       subroutine MyLineSearch(linesearch, lctx, ierr)
316: #include <finclude/petscsys.h>
317: #include <finclude/petscvec.h>
318: #include <finclude/petscmat.h>
319: #include <finclude/petscksp.h>
320: #include <finclude/petscpc.h>
321: #include <finclude/petscsnes.h>

323:       SNES              snes
324:       integer           lctx
325:       Vec               x, f,g, y, w
326:       PetscReal         ynorm,gnorm,xnorm
327:       PetscBool         flag
328:       PetscErrorCode    ierr

330:       PetscScalar       mone

332:       mone = -1.0d0
333:       call SNESLineSearchGetSNES(linesearch, snes, ierr)
334:       call SNESLineSearchGetVecs(linesearch, x, f, y, w, g, ierr)
335:       call VecNorm(y,NORM_2,ynorm,ierr)
336:       call VecAXPY(x,mone,y,ierr)
337:       call SNESComputeFunction(snes,x,f,ierr)
338:       call VecNorm(f,NORM_2,gnorm,ierr)
339:       call VecNorm(x,NORM_2,xnorm,ierr)
340:       call VecNorm(y,NORM_2,ynorm,ierr)
341:       call SNESLineSearchSetNorms(linesearch, xnorm, gnorm, ynorm,      &
342:      & ierr)
343:       flag = PETSC_FALSE
344:       return
345:       end