Actual source code: ex2.c
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 */
13: PetscInt n = 10, i, its, col[3];
14: PetscScalar value[3];
15: PCType pcname;
16: KSPType kspname;
17: PetscReal norm, tol = 1000. * PETSC_MACHINE_EPSILON;
19: PetscFunctionBeginUser;
20: PetscCall(PetscInitialize(&argc, &args, (char *)0, help));
21: /* Create and initialize vectors */
22: PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &b));
23: PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &ustar));
24: PetscCall(VecCreateSeq(PETSC_COMM_SELF, n, &u));
25: PetscCall(VecSet(ustar, 1.0));
26: PetscCall(VecSet(u, 0.0));
28: /* Create and assemble matrix */
29: PetscCall(MatCreateSeqAIJ(PETSC_COMM_SELF, n, n, 3, NULL, &mat));
30: value[0] = -1.0;
31: value[1] = 2.0;
32: value[2] = -1.0;
33: for (i = 1; i < n - 1; i++) {
34: col[0] = i - 1;
35: col[1] = i;
36: col[2] = i + 1;
37: PetscCall(MatSetValues(mat, 1, &i, 3, col, value, INSERT_VALUES));
38: }
39: i = n - 1;
40: col[0] = n - 2;
41: col[1] = n - 1;
42: PetscCall(MatSetValues(mat, 1, &i, 2, col, value, INSERT_VALUES));
43: i = 0;
44: col[0] = 0;
45: col[1] = 1;
46: value[0] = 2.0;
47: value[1] = -1.0;
48: PetscCall(MatSetValues(mat, 1, &i, 2, col, value, INSERT_VALUES));
49: PetscCall(MatAssemblyBegin(mat, MAT_FINAL_ASSEMBLY));
50: PetscCall(MatAssemblyEnd(mat, MAT_FINAL_ASSEMBLY));
52: /* Compute right-hand-side vector */
53: PetscCall(MatMult(mat, ustar, b));
55: /* Create PC context and set up data structures */
56: PetscCall(PCCreate(PETSC_COMM_WORLD, &pc));
57: PetscCall(PCSetType(pc, PCNONE));
58: PetscCall(PCSetFromOptions(pc));
59: PetscCall(PCSetOperators(pc, mat, mat));
60: PetscCall(PCSetUp(pc));
62: /* Create KSP context and set up data structures */
63: PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp));
64: PetscCall(KSPSetType(ksp, KSPRICHARDSON));
65: PetscCall(KSPSetFromOptions(ksp));
66: PetscCall(PCSetOperators(pc, mat, mat));
67: PetscCall(KSPSetPC(ksp, pc));
68: PetscCall(KSPSetUp(ksp));
70: /* Solve the problem */
71: PetscCall(KSPGetType(ksp, &kspname));
72: PetscCall(PCGetType(pc, &pcname));
73: PetscCall(PetscPrintf(PETSC_COMM_SELF, "Running %s with %s preconditioning\n", kspname, pcname));
74: PetscCall(KSPSolve(ksp, b, u));
75: PetscCall(VecAXPY(u, -1.0, ustar));
76: PetscCall(VecNorm(u, NORM_2, &norm));
77: PetscCall(KSPGetIterationNumber(ksp, &its));
78: if (norm > tol) PetscCall(PetscPrintf(PETSC_COMM_SELF, "2 norm of error %g Number of iterations %" PetscInt_FMT "\n", (double)norm, its));
80: /* Free data structures */
81: PetscCall(KSPDestroy(&ksp));
82: PetscCall(VecDestroy(&u));
83: PetscCall(VecDestroy(&ustar));
84: PetscCall(VecDestroy(&b));
85: PetscCall(MatDestroy(&mat));
86: PetscCall(PCDestroy(&pc));
88: PetscCall(PetscFinalize());
89: return 0;
90: }
92: /*TEST
94: test:
95: args: -ksp_type cg -ksp_monitor_short
97: TEST*/