Actual source code: ex8f.F
petsc-3.3-p6 2013-02-11
1: !
2: ! Tests PCMGSetResidual
3: !
4: ! -----------------------------------------------------------------------
6: program main
7: implicit none
9: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
10: ! Include files
11: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
12: !
13: !
14: #include <finclude/petscsys.h>
15: #include <finclude/petscvec.h>
16: #include <finclude/petscmat.h>
17: #include <finclude/petscpc.h>
18: #include <finclude/petscksp.h>
19: #include <finclude/petscpcmg.h>
20: !
21: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
22: ! Variable declarations
23: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
24: !
25: ! Variables:
26: ! ksp - linear solver context
27: ! x, b, u - approx solution, right-hand-side, exact solution vectors
28: ! A - matrix that defines linear system
29: ! its - iterations for convergence
30: ! norm - norm of error in solution
31: ! rctx - random number context
32: !
34: Mat A
35: Vec x,b,u
36: PC pc
37: PetscInt n,dim,istart,iend
38: PetscInt i,j,jj,ii,one,zero
39: PetscErrorCode ierr
40: PetscScalar v
41: external MyResidual
42: PetscScalar pfive
43: KSP ksp
45: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
46: ! Beginning of program
47: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
49: call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
50: pfive = .5d0
51: n = 6
52: dim = n*n
53: one = 1
54: zero = 0
56: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
57: ! Compute the matrix and right-hand-side vector that define
58: ! the linear system, Ax = b.
59: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
61: ! Create parallel matrix, specifying only its global dimensions.
62: ! When using MatCreate(), the matrix format can be specified at
63: ! runtime. Also, the parallel partitioning of the matrix is
64: ! determined by PETSc at runtime.
66: call MatCreate(PETSC_COMM_WORLD,A,ierr)
67: call MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,dim,dim,ierr)
68: call MatSetFromOptions(A,ierr)
69: call MatSetUp(A,ierr)
71: ! Currently, all PETSc parallel matrix formats are partitioned by
72: ! contiguous chunks of rows across the processors. Determine which
73: ! rows of the matrix are locally owned.
75: call MatGetOwnershipRange(A,Istart,Iend,ierr)
77: ! Set matrix elements in parallel.
78: ! - Each processor needs to insert only elements that it owns
79: ! locally (but any non-local elements will be sent to the
80: ! appropriate processor during matrix assembly).
81: ! - Always specify global rows and columns of matrix entries.
83: do 10, II=Istart,Iend-1
84: v = -1.0
85: i = II/n
86: j = II - i*n
87: if (i.gt.0) then
88: JJ = II - n
89: call MatSetValues(A,one,II,one,JJ,v,ADD_VALUES,ierr)
90: endif
91: if (i.lt.n-1) then
92: JJ = II + n
93: call MatSetValues(A,one,II,one,JJ,v,ADD_VALUES,ierr)
94: endif
95: if (j.gt.0) then
96: JJ = II - 1
97: call MatSetValues(A,one,II,one,JJ,v,ADD_VALUES,ierr)
98: endif
99: if (j.lt.n-1) then
100: JJ = II + 1
101: call MatSetValues(A,one,II,one,JJ,v,ADD_VALUES,ierr)
102: endif
103: v = 4.0
104: call MatSetValues(A,one,II,one,II,v,ADD_VALUES,ierr)
105: 10 continue
107: ! Assemble matrix, using the 2-step process:
108: ! MatAssemblyBegin(), MatAssemblyEnd()
109: ! Computations can be done while messages are in transition
110: ! by placing code between these two statements.
112: call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr)
113: call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr)
115: ! Create parallel vectors.
116: ! - Here, the parallel partitioning of the vector is determined by
117: ! PETSc at runtime. We could also specify the local dimensions
118: ! if desired.
119: ! - Note: We form 1 vector from scratch and then duplicate as needed.
121: call VecCreate(PETSC_COMM_WORLD,u,ierr)
122: call VecSetSizes(u,PETSC_DECIDE,dim,ierr)
123: call VecSetFromOptions(u,ierr)
124: call VecDuplicate(u,b,ierr)
125: call VecDuplicate(b,x,ierr)
127: ! Set exact solution; then compute right-hand-side vector.
129: call VecSet(u,pfive,ierr)
130: call MatMult(A,u,b,ierr)
132: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
133: ! Create the linear solver and set various options
134: ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
136: ! Create linear solver context
138: call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)
139: call KSPGetPC(ksp,pc,ierr)
140: call PCSetType(pc,PCMG,ierr)
141: call PCMGSetLevels(pc,one,PETSC_NULL_OBJECT,ierr)
142: call PCMGSetResidual(pc,zero,PCMGDefaultResidual,A,ierr)
144: call PCMGSetResidual(pc,zero,MyResidual,A,ierr)
146: ! Set operators. Here the matrix that defines the linear system
147: ! also serves as the preconditioning matrix.
149: call KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN,ierr)
152: call KSPDestroy(ksp,ierr)
153: call VecDestroy(u,ierr)
154: call VecDestroy(x,ierr)
155: call VecDestroy(b,ierr)
156: call MatDestroy(A,ierr)
158: call PetscFinalize(ierr)
159: end
161: subroutine MyResidual(A,b,x,r,ierr)
162: Mat A
163: Vec b,x,r
164: integer ierr
165: return
166: end