Actual source code: ex15.c
2: static char help[] = "KSP on an operator with a null space.\n\n";
4: #include petscksp.h
8: int main(int argc,char **args)
9: {
10: Vec x,b,u; /* approx solution, RHS, exact solution */
11: Mat A; /* linear system matrix */
12: KSP ksp; /* KSP context */
14: PetscInt i,n = 10,col[3],its,i1,i2;
15: PetscScalar none = -1.0,value[3],avalue;
16: PetscReal norm;
17: PC pc;
19: PetscInitialize(&argc,&args,(char *)0,help);
20: PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);
22: /* Create vectors */
23: VecCreate(PETSC_COMM_WORLD,&x);
24: VecSetSizes(x,PETSC_DECIDE,n);
25: VecSetFromOptions(x);
26: VecDuplicate(x,&b);
27: VecDuplicate(x,&u);
29: /* create a solution that is orthogonal to the constants */
30: VecGetOwnershipRange(u,&i1,&i2);
31: for (i=i1; i<i2; i++) {
32: avalue = i;
33: VecSetValues(u,1,&i,&avalue,INSERT_VALUES);
34: }
35: VecAssemblyBegin(u);
36: VecAssemblyEnd(u);
37: VecSum(u,&avalue);
38: avalue = -avalue/(PetscReal)n;
39: VecShift(u,avalue);
41: /* Create and assemble matrix */
42: MatCreate(PETSC_COMM_WORLD,&A);
43: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n,n);
44: MatSetFromOptions(A);
45: value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
46: for (i=1; i<n-1; i++) {
47: col[0] = i-1; col[1] = i; col[2] = i+1;
48: MatSetValues(A,1,&i,3,col,value,INSERT_VALUES);
49: }
50: i = n - 1; col[0] = n - 2; col[1] = n - 1; value[1] = 1.0;
51: MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
52: i = 0; col[0] = 0; col[1] = 1; value[0] = 1.0; value[1] = -1.0;
53: MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
54: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
55: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
56: MatMult(A,u,b);
58: /* Create KSP context; set operators and options; solve linear system */
59: KSPCreate(PETSC_COMM_WORLD,&ksp);
60: KSPSetOperators(ksp,A,A,DIFFERENT_NONZERO_PATTERN);
62: /* Insure that preconditioner has same null space as matrix */
63: /* currently does not do anything */
64: KSPGetPC(ksp,&pc);
66: KSPSetFromOptions(ksp);
67: KSPSolve(ksp,b,x);
68: /* KSPView(ksp,PETSC_VIEWER_STDOUT_WORLD); */
70: /* Check error */
71: VecAXPY(x,none,u);
72: VecNorm(x,NORM_2,&norm);
73: KSPGetIterationNumber(ksp,&its);
74: PetscPrintf(PETSC_COMM_WORLD,"Norm of error %A, Iterations %D\n",norm,its);
76: /* Free work space */
77: VecDestroy(x);VecDestroy(u);
78: VecDestroy(b);MatDestroy(A);
79: KSPDestroy(ksp);
80: PetscFinalize();
81: return 0;
82: }