Actual source code: ex15.c
1: /*$Id: ex15.c,v 1.28 2001/08/07 21:30:50 bsmith Exp $*/
3: static char help[] = "SLES on an operator with a null space.nn";
5: #include petscsles.h
7: int main(int argc,char **args)
8: {
9: Vec x,b,u; /* approx solution, RHS, exact solution */
10: Mat A; /* linear system matrix */
11: SLES sles; /* SLES context */
12: int ierr,i,n = 10,col[3],its,i1,i2;
13: PetscScalar none = -1.0,value[3],avalue;
14: PetscReal norm;
15: PC pc;
17: PetscInitialize(&argc,&args,(char *)0,help);
18: PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);
20: /* Create vectors */
21: VecCreate(PETSC_COMM_WORLD,&x);
22: VecSetSizes(x,PETSC_DECIDE,n);
23: VecSetFromOptions(x);
24: VecDuplicate(x,&b);
25: VecDuplicate(x,&u);
27: /* create a solution that is orthogonal to the constants */
28: VecGetOwnershipRange(u,&i1,&i2);
29: for (i=i1; i<i2; i++) {
30: avalue = i;
31: VecSetValues(u,1,&i,&avalue,INSERT_VALUES);
32: }
33: VecAssemblyBegin(u);
34: VecAssemblyEnd(u);
35: VecSum(u,&avalue);
36: avalue = -avalue/(PetscReal)n;
37: VecShift(&avalue,u);
39: /* Create and assemble matrix */
40: MatCreate(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,n,n,&A);
41: MatSetFromOptions(A);
42: value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
43: for (i=1; i<n-1; i++) {
44: col[0] = i-1; col[1] = i; col[2] = i+1;
45: MatSetValues(A,1,&i,3,col,value,INSERT_VALUES);
46: }
47: i = n - 1; col[0] = n - 2; col[1] = n - 1; value[1] = 1.0;
48: MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
49: i = 0; col[0] = 0; col[1] = 1; value[0] = 1.0; value[1] = -1.0;
50: MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
51: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
52: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
53: MatMult(A,u,b);
55: /* Create SLES context; set operators and options; solve linear system */
56: SLESCreate(PETSC_COMM_WORLD,&sles);
57: SLESSetOperators(sles,A,A,DIFFERENT_NONZERO_PATTERN);
59: /* Insure that preconditioner has same null space as matrix */
60: SLESGetPC(sles,&pc);
62: SLESSetFromOptions(sles);
63: SLESSolve(sles,b,x,&its);
64: /* SLESView(sles,PETSC_VIEWER_STDOUT_WORLD); */
66: /* Check error */
67: VecAXPY(&none,u,x);
68: VecNorm(x,NORM_2,&norm);
69: PetscPrintf(PETSC_COMM_WORLD,"Norm of error %A, Iterations %dn",norm,its);
71: /* Free work space */
72: VecDestroy(x);VecDestroy(u);
73: VecDestroy(b);MatDestroy(A);
74: SLESDestroy(sles);
75: PetscFinalize();
76: return 0;
77: }