Actual source code: ex12f.F
1: !
2: !
3: ! This example demonstrates basic use of the SNES Fortran interface.
4: !
5: ! Note: The program ex10.f is the same as this example, except that it
6: ! uses the Fortran .f suffix rather than the .F suffix.
7: !
8: ! In this example the application context is a Fortran integer array:
9: ! ctx(1) = da - distributed array
10: ! 2 = F - global vector where the function is stored
11: ! 3 = xl - local work vector
12: ! 4 = rank - processor rank
13: ! 5 = size - number of processors
14: ! 6 = N - system size
15: !
16: ! Note: Any user-defined Fortran routines (such as FormJacobian)
17: ! MUST be declared as external.
18: !
19: !
20: ! Macros to make setting/getting values into vector clearer.
21: ! The element xx(ib) is the ibth element in the vector indicated by ctx(3)
22: #define xx(ib) vxx(ixx + (ib))
23: #define ff(ib) vff(iff + (ib))
24: #define F2(ib) vF2(iF2 + (ib))
25: program main
26: implicit none
28: #include finclude/petscsys.h
29: #include finclude/petscvec.h
30: #include finclude/petscda.h
31: #include finclude/petscmat.h
32: #include finclude/petscsnes.h
34: PetscFortranAddr ctx(6)
35: PetscMPIInt rank,size
36: PetscErrorCode ierr
37: PetscInt N,start,end,nn,i
38: PetscInt ii,its,i1,i0,i3
39: PetscTruth flg
40: SNES snes
41: Mat J
42: Vec x,r,u
43: PetscScalar xp,FF,UU,h
44: character*(10) matrixname
45: external FormJacobian,FormFunction
47: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
48: i1 = 1
49: i0 = 0
50: i3 = 3
51: N = 10
52: call PetscOptionsGetInt(PETSC_NULL_CHARACTER,'-n',N,flg,ierr)
53: h = 1.d0/(N-1.d0)
54: ctx(6) = N
56: call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)
57: call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
58: ctx(4) = rank
59: ctx(5) = size
61: ! Set up data structures
62: call DACreate1d(PETSC_COMM_WORLD,DA_NONPERIODIC,N,i1,i1, &
63: & PETSC_NULL_INTEGER,ctx(1),ierr)
65: call DACreateGlobalVector(ctx(1),x,ierr)
66: call DACreateLocalVector(ctx(1),ctx(3),ierr)
68: call PetscObjectSetName(x,'Approximate Solution',ierr)
69: call VecDuplicate(x,r,ierr)
70: call VecDuplicate(x,ctx(2),ierr)
71: call VecDuplicate(x,U,ierr)
72: call PetscObjectSetName(U,'Exact Solution',ierr)
74: call MatCreateMPIAIJ(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,N, &
75: & N,i3,PETSC_NULL_INTEGER,i0,PETSC_NULL_INTEGER,J,ierr)
77: call MatGetType(J,matrixname,ierr)
79: ! Store right-hand-side of PDE and exact solution
80: call VecGetOwnershipRange(x,start,end,ierr)
81: xp = h*start
82: nn = end - start
83: ii = start
84: do 10, i=0,nn-1
85: FF = 6.0*xp + (xp+1.e-12)**6.e0
86: UU = xp*xp*xp
87: call VecSetValues(ctx(2),i1,ii,FF,INSERT_VALUES,ierr)
88: call VecSetValues(U,i1,ii,UU,INSERT_VALUES,ierr)
89: xp = xp + h
90: ii = ii + 1
91: 10 continue
92: call VecAssemblyBegin(ctx(2),ierr)
93: call VecAssemblyEnd(ctx(2),ierr)
94: call VecAssemblyBegin(U,ierr)
95: call VecAssemblyEnd(U,ierr)
97: ! Create nonlinear solver
98: call SNESCreate(PETSC_COMM_WORLD,snes,ierr)
100: ! Set various routines and options
101: call SNESSetFunction(snes,r,FormFunction,ctx,ierr)
102: call SNESSetJacobian(snes,J,J,FormJacobian,ctx,ierr)
103: call SNESSetFromOptions(snes,ierr)
105: ! Solve nonlinear system
106: call FormInitialGuess(snes,x,ierr)
107: call SNESSolve(snes,PETSC_NULL_OBJECT,x,ierr)
108: call SNESGetIterationNumber(snes,its,ierr);
110: ! Write results if first processor
111: if (ctx(4) .eq. 0) then
112: write(6,100) its
113: endif
114: 100 format('Number of Newton iterations = ',i5)
116: ! Free work space. All PETSc objects should be destroyed when they
117: ! are no longer needed.
118: call VecDestroy(x,ierr)
119: call VecDestroy(ctx(3),ierr)
120: call VecDestroy(r,ierr)
121: call VecDestroy(U,ierr)
122: call VecDestroy(ctx(2),ierr)
123: call MatDestroy(J,ierr)
124: call SNESDestroy(snes,ierr)
125: call DADestroy(ctx(1),ierr)
126: call PetscFinalize(ierr)
127: end
130: ! -------------------- Evaluate Function F(x) ---------------------
132: subroutine FormFunction(snes,x,f,ctx,ierr)
133: implicit none
134: SNES snes
135: Vec x,f
136: PetscFortranAddr ctx(*)
137: PetscMPIInt rank,size
138: PetscInt i,s,n
139: PetscErrorCode ierr
140: PetscOffset ixx,iff,iF2
141: PetscScalar h,d,vf2(1),vxx(1),vff(1)
142: #include finclude/petscsys.h
143: #include finclude/petscvec.h
144: #include finclude/petscda.h
145: #include finclude/petscmat.h
146: #include finclude/petscsnes.h
149: rank = ctx(4)
150: size = ctx(5)
151: h = 1.d0/(ctx(6) - 1.d0)
152: call DAGlobalToLocalBegin(ctx(1),x,INSERT_VALUES,ctx(3),ierr)
153: call DAGlobalToLocalEnd(ctx(1),x,INSERT_VALUES,ctx(3),ierr)
155: call VecGetLocalSize(ctx(3),n,ierr)
156: if (n .gt. 1000) then
157: print*, 'Local work array not big enough'
158: call MPI_Abort(PETSC_COMM_WORLD,0,ierr)
159: endif
161: !
162: ! This sets the index ixx so that vxx(ixx+1) is the first local
163: ! element in the vector indicated by ctx(3).
164: !
165: call VecGetArray(ctx(3),vxx,ixx,ierr)
166: call VecGetArray(f,vff,iff,ierr)
167: call VecGetArray(ctx(2),vF2,iF2,ierr)
169: d = h*h
171: !
172: ! Note that the array vxx() was obtained from a ghosted local vector
173: ! ctx(3) while the array vff() was obtained from the non-ghosted parallel
174: ! vector F. This is why there is a need for shift variable s. Since vff()
175: ! does not have locations for the ghost variables we need to index in it
176: ! slightly different then indexing into vxx(). For example on processor
177: ! 1 (the second processor)
178: !
179: ! xx(1) xx(2) xx(3) .....
180: ! ^^^^^^^ ^^^^^ ^^^^^
181: ! ghost value 1st local value 2nd local value
182: !
183: ! ff(1) ff(2)
184: ! ^^^^^^^ ^^^^^^^
185: ! 1st local value 2nd local value
186: !
187: if (rank .eq. 0) then
188: s = 0
189: ff(1) = xx(1)
190: else
191: s = 1
192: endif
194: do 10 i=1,n-2
195: ff(i-s+1) = d*(xx(i) - 2.d0*xx(i+1) &
196: & + xx(i+2)) + xx(i+1)*xx(i+1) &
197: & - F2(i-s+1)
198: 10 continue
200: if (rank .eq. size-1) then
201: ff(n-s) = xx(n) - 1.d0
202: endif
204: call VecRestoreArray(f,vff,iff,ierr)
205: call VecRestoreArray(ctx(3),vxx,ixx,ierr)
206: call VecRestoreArray(ctx(2),vF2,iF2,ierr)
207: return
208: end
210: ! -------------------- Form initial approximation -----------------
212: subroutine FormInitialGuess(snes,x,ierr)
213: implicit none
214: #include finclude/petscsys.h
215: #include finclude/petscvec.h
216: #include finclude/petscsnes.h
217: PetscErrorCode ierr
218: Vec x
219: SNES snes
220: PetscScalar five
222: five = 5.d-1
223: call VecSet(x,five,ierr)
224: return
225: end
227: ! -------------------- Evaluate Jacobian --------------------
229: subroutine FormJacobian(snes,x,jac,B,flag,ctx,ierr)
230: implicit none
231: #include finclude/petscsys.h
232: #include finclude/petscvec.h
233: #include finclude/petscda.h
234: #include finclude/petscmat.h
235: #include finclude/petscsnes.h
236: SNES snes
237: Vec x
238: Mat jac,B
239: PetscFortranAddr ctx(*)
240: PetscTruth flag
241: PetscInt ii,istart,iend
242: PetscInt i,j,n,end,start,i1
243: PetscErrorCode ierr
244: PetscMPIInt rank,size
245: PetscOffset ixx
246: PetscScalar d,A,h,vxx(1)
248: i1 = 1
249: h = 1.d0/(ctx(6) - 1.d0)
250: d = h*h
251: rank = ctx(4)
252: size = ctx(5)
254: call VecGetArray(x,vxx,ixx,ierr)
255: call VecGetOwnershipRange(x,start,end,ierr)
256: n = end - start
258: if (rank .eq. 0) then
259: A = 1.0
260: call MatSetValues(jac,i1,start,i1,start,A,INSERT_VALUES,ierr)
261: istart = 1
262: else
263: istart = 0
264: endif
265: if (rank .eq. size-1) then
266: i = ctx(6)-1
267: A = 1.0
268: call MatSetValues(jac,i1,i,i1,i,A,INSERT_VALUES,ierr)
269: iend = n-1
270: else
271: iend = n
272: endif
273: do 10 i=istart,iend-1
274: ii = i + start
275: j = start + i - 1
276: call MatSetValues(jac,i1,ii,i1,j,d,INSERT_VALUES,ierr)
277: j = start + i + 1
278: call MatSetValues(jac,i1,ii,i1,j,d,INSERT_VALUES,ierr)
279: A = -2.0*d + 2.0*xx(i+1)
280: call MatSetValues(jac,i1,ii,i1,ii,A,INSERT_VALUES,ierr)
281: 10 continue
282: call VecRestoreArray(x,vxx,ixx,ierr)
283: call MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY,ierr)
284: call MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY,ierr)
285: return
286: end