Actual source code: ex2.c
petsc-3.8.4 2018-03-24
2: static char help[] = "Tests PC and KSP on a tridiagonal matrix. Note that most\n\
3: users should employ the KSP interface instead of using PC directly.\n\n";
5: #include <petscksp.h>
7: int main(int argc,char **args)
8: {
9: Mat mat; /* matrix */
10: Vec b,ustar,u; /* vectors (RHS, exact solution, approx solution) */
11: PC pc; /* PC context */
12: KSP ksp; /* KSP context */
14: PetscInt n = 10,i,its,col[3];
15: PetscScalar value[3];
16: PCType pcname;
17: KSPType kspname;
18: PetscReal norm,tol=1000.*PETSC_MACHINE_EPSILON;
20: PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
21: /* Create and initialize vectors */
22: VecCreateSeq(PETSC_COMM_SELF,n,&b);
23: VecCreateSeq(PETSC_COMM_SELF,n,&ustar);
24: VecCreateSeq(PETSC_COMM_SELF,n,&u);
25: VecSet(ustar,1.0);
26: VecSet(u,0.0);
28: /* Create and assemble matrix */
29: MatCreateSeqAIJ(PETSC_COMM_SELF,n,n,3,NULL,&mat);
30: value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
31: for (i=1; i<n-1; i++) {
32: col[0] = i-1; col[1] = i; col[2] = i+1;
33: MatSetValues(mat,1,&i,3,col,value,INSERT_VALUES);
34: }
35: i = n - 1; col[0] = n - 2; col[1] = n - 1;
36: MatSetValues(mat,1,&i,2,col,value,INSERT_VALUES);
37: i = 0; col[0] = 0; col[1] = 1; value[0] = 2.0; value[1] = -1.0;
38: MatSetValues(mat,1,&i,2,col,value,INSERT_VALUES);
39: MatAssemblyBegin(mat,MAT_FINAL_ASSEMBLY);
40: MatAssemblyEnd(mat,MAT_FINAL_ASSEMBLY);
42: /* Compute right-hand-side vector */
43: MatMult(mat,ustar,b);
45: /* Create PC context and set up data structures */
46: PCCreate(PETSC_COMM_WORLD,&pc);
47: PCSetType(pc,PCNONE);
48: PCSetFromOptions(pc);
49: PCSetOperators(pc,mat,mat);
50: PCSetUp(pc);
52: /* Create KSP context and set up data structures */
53: KSPCreate(PETSC_COMM_WORLD,&ksp);
54: KSPSetType(ksp,KSPRICHARDSON);
55: KSPSetFromOptions(ksp);
56: PCSetOperators(pc,mat,mat);
57: KSPSetPC(ksp,pc);
58: KSPSetUp(ksp);
60: /* Solve the problem */
61: KSPGetType(ksp,&kspname);
62: PCGetType(pc,&pcname);
63: PetscPrintf(PETSC_COMM_SELF,"Running %s with %s preconditioning\n",kspname,pcname);
64: KSPSolve(ksp,b,u);
65: VecAXPY(u,-1.0,ustar);
66: VecNorm(u,NORM_2,&norm);
67: KSPGetIterationNumber(ksp,&its);
68: if (norm > tol) {
69: PetscPrintf(PETSC_COMM_SELF,"2 norm of error %g Number of iterations %D\n",(double)norm,its);
70: }
72: /* Free data structures */
73: KSPDestroy(&ksp);
74: VecDestroy(&u);
75: VecDestroy(&ustar);
76: VecDestroy(&b);
77: MatDestroy(&mat);
78: PCDestroy(&pc);
80: PetscFinalize();
81: return ierr;
82: }