1 static char help[] = "Tests PC and KSP on a tridiagonal matrix. Note that most\n\
2 users should employ the KSP interface instead of using PC directly.\n\n";
3
4 #include <petscksp.h>
5
main(int argc,char ** args)6 int main(int argc, char **args)
7 {
8 Mat mat; /* matrix */
9 Vec b, ustar, u; /* vectors (RHS, exact solution, approx solution) */
10 PC pc; /* PC context */
11 KSP ksp; /* KSP context */
12 PetscInt n = 10, i, its, col[3];
13 PetscScalar value[3];
14 PCType pcname;
15 KSPType kspname;
16 PetscReal norm, tol = 1000. * PETSC_MACHINE_EPSILON;
17
18 PetscFunctionBeginUser;
19 PetscCall(PetscInitialize(&argc, &args, NULL, help));
20 /* Create and initialize vectors */
21 PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &b));
22 PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &ustar));
23 PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &u));
24 PetscCall(VecSet(ustar, 1.0));
25 PetscCall(VecSet(u, 0.0));
26
27 /* Create and assemble matrix */
28 PetscCall(MatCreateSeqAIJ(PETSC_COMM_SELF, n, n, 3, NULL, &mat));
29 value[0] = -1.0;
30 value[1] = 2.0;
31 value[2] = -1.0;
32 for (i = 1; i < n - 1; i++) {
33 col[0] = i - 1;
34 col[1] = i;
35 col[2] = i + 1;
36 PetscCall(MatSetValues(mat, 1, &i, 3, col, value, INSERT_VALUES));
37 }
38 i = n - 1;
39 col[0] = n - 2;
40 col[1] = n - 1;
41 PetscCall(MatSetValues(mat, 1, &i, 2, col, value, INSERT_VALUES));
42 i = 0;
43 col[0] = 0;
44 col[1] = 1;
45 value[0] = 2.0;
46 value[1] = -1.0;
47 PetscCall(MatSetValues(mat, 1, &i, 2, col, value, INSERT_VALUES));
48 PetscCall(MatAssemblyBegin(mat, MAT_FINAL_ASSEMBLY));
49 PetscCall(MatAssemblyEnd(mat, MAT_FINAL_ASSEMBLY));
50
51 /* Compute right-hand-side vector */
52 PetscCall(MatMult(mat, ustar, b));
53
54 /* Create PC context and set up data structures */
55 PetscCall(PCCreate(PETSC_COMM_WORLD, &pc));
56 PetscCall(PCSetType(pc, PCNONE));
57 PetscCall(PCSetFromOptions(pc));
58 PetscCall(PCSetOperators(pc, mat, mat));
59 PetscCall(PCSetUp(pc));
60
61 /* Create KSP context and set up data structures */
62 PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp));
63 PetscCall(KSPSetType(ksp, KSPRICHARDSON));
64 PetscCall(KSPSetFromOptions(ksp));
65 PetscCall(PCSetOperators(pc, mat, mat));
66 PetscCall(KSPSetPC(ksp, pc));
67 PetscCall(KSPSetUp(ksp));
68
69 /* Solve the problem */
70 PetscCall(KSPGetType(ksp, &kspname));
71 PetscCall(PCGetType(pc, &pcname));
72 PetscCall(PetscPrintf(PETSC_COMM_SELF, "Running %s with %s preconditioning\n", kspname, pcname));
73 PetscCall(KSPSolve(ksp, b, u));
74 PetscCall(VecAXPY(u, -1.0, ustar));
75 PetscCall(VecNorm(u, NORM_2, &norm));
76 PetscCall(KSPGetIterationNumber(ksp, &its));
77 if (norm > tol) PetscCall(PetscPrintf(PETSC_COMM_SELF, "2 norm of error %g Number of iterations %" PetscInt_FMT "\n", (double)norm, its));
78
79 /* Free data structures */
80 PetscCall(KSPDestroy(&ksp));
81 PetscCall(VecDestroy(&u));
82 PetscCall(VecDestroy(&ustar));
83 PetscCall(VecDestroy(&b));
84 PetscCall(MatDestroy(&mat));
85 PetscCall(PCDestroy(&pc));
86
87 PetscCall(PetscFinalize());
88 return 0;
89 }
90
91 /*TEST
92
93 test:
94 args: -ksp_type cg -ksp_monitor_short
95
96 TEST*/
97