Actual source code: ex70.c
1: static char help[] = "Solves an ill-conditioned tridiagonal linear system with KSP for testing GMRES breakdown tolerance.\n\n";
3: #include <petscksp.h>
5: int main(int argc, char **args)
6: {
7: Vec x, b, u; /* approx solution, RHS, exact solution */
8: Mat A; /* linear system matrix */
9: KSP ksp; /* linear solver context */
10: PetscInt i, n = 10, col[3];
11: PetscMPIInt size;
12: PetscScalar value[3];
14: PetscFunctionBeginUser;
15: PetscCall(PetscInitialize(&argc, &args, (char *)0, help));
16: PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
17: PetscCheck(size == 1, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "This is a uniprocessor example only!");
19: /*
20: Create vectors. Note that we form 1 vector from scratch and
21: then duplicate as needed.
22: */
23: PetscCall(VecCreate(PETSC_COMM_WORLD, &x));
24: PetscCall(PetscObjectSetName((PetscObject)x, "Solution"));
25: PetscCall(VecSetSizes(x, PETSC_DECIDE, n));
26: PetscCall(VecSetFromOptions(x));
27: PetscCall(VecDuplicate(x, &b));
28: PetscCall(VecDuplicate(x, &u));
30: PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
31: PetscCall(MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, n, n));
32: PetscCall(MatSetFromOptions(A));
33: PetscCall(MatSetUp(A));
35: /*
36: Set big off-diag values to make the system ill-conditioned
37: */
38: value[0] = 10.0;
39: value[1] = 2.0;
40: value[2] = 1.0;
41: for (i = 1; i < n - 1; i++) {
42: col[0] = i - 1;
43: col[1] = i;
44: col[2] = i + 1;
45: PetscCall(MatSetValues(A, 1, &i, 3, col, value, INSERT_VALUES));
46: }
47: i = n - 1;
48: col[0] = n - 2;
49: col[1] = n - 1;
50: PetscCall(MatSetValues(A, 1, &i, 2, col, value, INSERT_VALUES));
51: i = 0;
52: col[0] = 0;
53: col[1] = 1;
54: value[0] = 2.0;
55: value[1] = -1.0;
56: PetscCall(MatSetValues(A, 1, &i, 2, col, value, INSERT_VALUES));
57: PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
58: PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
60: PetscCall(VecSet(u, 1.0));
61: PetscCall(MatMult(A, u, b));
63: PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp));
64: PetscCall(KSPSetOperators(ksp, A, A));
65: PetscCall(KSPSetFromOptions(ksp));
66: PetscCall(KSPSolve(ksp, b, x));
68: PetscCall(KSPSetInitialGuessNonzero(ksp, PETSC_TRUE));
69: PetscCall(PetscOptionsInsertString(NULL, "-ksp_type preonly -ksp_initial_guess_nonzero false"));
70: PetscCall(PetscOptionsClearValue(NULL, "-ksp_converged_reason"));
71: PetscCall(KSPSetFromOptions(ksp));
72: PetscCall(KSPSolve(ksp, b, x));
74: PetscCall(VecDestroy(&x));
75: PetscCall(VecDestroy(&u));
76: PetscCall(VecDestroy(&b));
77: PetscCall(MatDestroy(&A));
78: PetscCall(KSPDestroy(&ksp));
80: PetscCall(PetscFinalize());
81: return 0;
82: }
84: /*TEST
86: test:
87: requires: double !complex
88: args: -ksp_rtol 1e-18 -pc_type sor -ksp_converged_reason -ksp_gmres_breakdown_tolerance 1.e-9
89: output_file: output/ex70.out
91: TEST*/