Actual source code: ex2.c
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";
4: #include <petscksp.h>
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;
18: PetscFunctionBeginUser;
19: PetscCall(PetscInitialize(&argc, &args, (char *)0, 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));
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));
51: /* Compute right-hand-side vector */
52: PetscCall(MatMult(mat, ustar, b));
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));
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));
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));
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));
87: PetscCall(PetscFinalize());
88: return 0;
89: }
91: /*TEST
93: test:
94: args: -ksp_type cg -ksp_monitor_short
96: TEST*/