Actual source code: ex15.c
1: /*$Id: ex15.c,v 1.26 2001/03/23 23:23:50 balay 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: Scalar none = -1.0,value[3],avalue;
14: double 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,PETSC_DECIDE,n,&x);
22: VecSetFromOptions(x);
23: VecDuplicate(x,&b);
24: VecDuplicate(x,&u);
26: /* create a solution that is orthogonal to the constants */
27: VecGetOwnershipRange(u,&i1,&i2);
28: for (i=i1; i<i2; i++) {
29: avalue = i;
30: VecSetValues(u,1,&i,&avalue,INSERT_VALUES);
31: }
32: VecAssemblyBegin(u);
33: VecAssemblyEnd(u);
34: VecSum(u,&avalue);
35: avalue = -avalue/(double)n;
36: VecShift(&avalue,u);
38: /* Create and assemble matrix */
39: MatCreate(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,n,n,&A);
40: MatSetFromOptions(A);
41: value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
42: for (i=1; i<n-1; i++) {
43: col[0] = i-1; col[1] = i; col[2] = i+1;
44: MatSetValues(A,1,&i,3,col,value,INSERT_VALUES);
45: }
46: i = n - 1; col[0] = n - 2; col[1] = n - 1; value[1] = 1.0;
47: MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
48: i = 0; col[0] = 0; col[1] = 1; value[0] = 1.0; value[1] = -1.0;
49: MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
50: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
51: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
52: MatMult(A,u,b);
54: /* Create SLES context; set operators and options; solve linear system */
55: SLESCreate(PETSC_COMM_WORLD,&sles);
56: SLESSetOperators(sles,A,A,DIFFERENT_NONZERO_PATTERN);
58: /* Insure that preconditioner has same null space as matrix */
59: SLESGetPC(sles,&pc);
61: SLESSetFromOptions(sles);
62: SLESSolve(sles,b,x,&its);
63: /* SLESView(sles,PETSC_VIEWER_STDOUT_WORLD); */
65: /* Check error */
66: VecAXPY(&none,u,x);
67: VecNorm(x,NORM_2,&norm);
68: PetscPrintf(PETSC_COMM_WORLD,"Norm of error %A, Iterations %dn",norm,its);
70: /* Free work space */
71: VecDestroy(x);VecDestroy(u);
72: VecDestroy(b);MatDestroy(A);
73: SLESDestroy(sles);
74: PetscFinalize();
75: return 0;
76: }