Actual source code: ex1f.F
petsc-3.6.1 2015-08-06
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_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 <petsc/finclude/petscsys.h>
208: #include <petsc/finclude/petscvec.h>
209: #include <petsc/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 VecGetArrayRead(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 VecRestoreArrayRead(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 <petsc/finclude/petscsys.h>
265: #include <petsc/finclude/petscvec.h>
266: #include <petsc/finclude/petscmat.h>
267: #include <petsc/finclude/petscpc.h>
268: #include <petsc/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 VecGetArrayRead(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 VecRestoreArrayRead(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 <petsc/finclude/petscsys.h>
317: #include <petsc/finclude/petscvec.h>
318: #include <petsc/finclude/petscmat.h>
319: #include <petsc/finclude/petscksp.h>
320: #include <petsc/finclude/petscpc.h>
321: #include <petsc/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