Actual source code: ex1f.F

petsc-master 2016-02-12
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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 <petsc/finclude/petscsys.h>
 33: #include <petsc/finclude/petscvec.h>
 34: #include <petsc/finclude/petscmat.h>
 35: #include <petsc/finclude/petscksp.h>
 36: #include <petsc/finclude/petscpc.h>
 37: #include <petsc/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_OBJECT,PETSC_NULL_CHARACTER,   &
154:      &                         '-setls',setls,ierr)

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

163: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
164: !  Evaluate initial guess; then solve nonlinear system
165: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

172:       pfive = 0.5
173:       call VecSet(x,pfive,ierr)
174:       call SNESSolve(snes,PETSC_NULL_OBJECT,x,ierr)
175:       call SNESGetIterationNumber(snes,its,ierr);
176:       if (rank .eq. 0) then
177:          write(6,100) its
178:       endif
179:   100 format('Number of SNES iterations = ',i5)

181: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
182: !  Free work space.  All PETSc objects should be destroyed when they
183: !  are no longer needed.
184: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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

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

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

217: !  Declarations for use with local arrays

219:       PetscScalar  lx_v(2),lf_v(2)
220:       PetscOffset  lx_i,lf_i

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

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

233: !  Compute function

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

240: !  Restore vectors

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

245:       return
246:       end

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

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

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

279: !  Declarations for use with local arrays

281:       PetscScalar lx_v(1)
282:       PetscOffset lx_i

284: !  Get pointer to vector data

286:       i2 = 2
287:       call VecGetArrayRead(x,lx_v,lx_i,ierr)

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

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

303: !  Restore vector

305:       call VecRestoreArrayRead(x,lx_v,lx_i,ierr)

307: !  Assemble matrix

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

312:       return
313:       end


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

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

331:       PetscScalar       mone

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