Actual source code: ex6.c
1: static char help[] = "Solves a tridiagonal linear system with KSP. \n\
2: It illustrates how to do one symbolic factorization and multiple numeric factorizations using same matrix nonzero structure. \n\n";
4: #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: PC pc; /* preconditioner context */
11: PetscReal norm; /* norm of solution error */
12: PetscInt i, col[3], its, rstart, rend, N = 10, num_numfac;
13: PetscScalar value[3];
15: PetscFunctionBeginUser;
16: PetscCall(PetscInitialize(&argc, &args, NULL, help));
17: PetscCall(PetscOptionsGetInt(NULL, NULL, "-N", &N, NULL));
19: /* Create and assemble matrix. */
20: PetscCall(MatCreate(PETSC_COMM_WORLD, &A));
21: PetscCall(MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, N, N));
22: PetscCall(MatSetFromOptions(A));
23: PetscCall(MatSetUp(A));
24: PetscCall(MatGetOwnershipRange(A, &rstart, &rend));
26: value[0] = -1.0;
27: value[1] = 2.0;
28: value[2] = -1.0;
29: for (i = rstart; i < rend; i++) {
30: col[0] = i - 1;
31: col[1] = i;
32: col[2] = i + 1;
33: if (i == 0) {
34: PetscCall(MatSetValues(A, 1, &i, 2, col + 1, value + 1, INSERT_VALUES));
35: } else if (i == N - 1) {
36: PetscCall(MatSetValues(A, 1, &i, 2, col, value, INSERT_VALUES));
37: } else {
38: PetscCall(MatSetValues(A, 1, &i, 3, col, value, INSERT_VALUES));
39: }
40: }
41: PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
42: PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
43: PetscCall(MatSetOption(A, MAT_NEW_NONZERO_LOCATION_ERR, PETSC_TRUE));
45: /* Create vectors */
46: PetscCall(MatCreateVecs(A, &x, &b));
47: PetscCall(VecDuplicate(x, &u));
49: /* Set exact solution; then compute right-hand-side vector. */
50: PetscCall(VecSet(u, 1.0));
51: PetscCall(MatMult(A, u, b));
53: /* Create the linear solver and set various options. */
54: PetscCall(KSPCreate(PETSC_COMM_WORLD, &ksp));
55: PetscCall(KSPGetPC(ksp, &pc));
56: PetscCall(PCSetType(pc, PCJACOBI));
57: PetscCall(KSPSetTolerances(ksp, 1.e-5, PETSC_CURRENT, PETSC_CURRENT, PETSC_CURRENT));
58: PetscCall(KSPSetOperators(ksp, A, A));
59: PetscCall(KSPSetFromOptions(ksp));
61: num_numfac = 1;
62: PetscCall(PetscOptionsGetInt(NULL, NULL, "-num_numfac", &num_numfac, NULL));
63: while (num_numfac--) {
64: /* An example on how to update matrix A for repeated numerical factorization and solve. */
65: PetscScalar one = 1.0;
66: PetscInt i = 0;
67: PetscCall(MatSetValues(A, 1, &i, 1, &i, &one, ADD_VALUES));
68: PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
69: PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
70: /* Update b */
71: PetscCall(MatMult(A, u, b));
73: /* Solve the linear system */
74: PetscCall(KSPSolve(ksp, b, x));
76: /* Check the solution and clean up */
77: PetscCall(VecAXPY(x, -1.0, u));
78: PetscCall(VecNorm(x, NORM_2, &norm));
79: PetscCall(KSPGetIterationNumber(ksp, &its));
80: if (norm > 100 * PETSC_MACHINE_EPSILON) PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Norm of error %g, Iterations %" PetscInt_FMT "\n", (double)norm, its));
81: }
83: /* Free work space. */
84: PetscCall(VecDestroy(&x));
85: PetscCall(VecDestroy(&u));
86: PetscCall(VecDestroy(&b));
87: PetscCall(MatDestroy(&A));
88: PetscCall(KSPDestroy(&ksp));
90: PetscCall(PetscFinalize());
91: return 0;
92: }
94: /*TEST
96: test:
97: args: -num_numfac 2 -pc_type lu
99: test:
100: suffix: 2
101: args: -num_numfac 2 -pc_type lu -pc_factor_mat_solver_type mumps
102: requires: mumps
104: test:
105: suffix: 3
106: nsize: 3
107: args: -num_numfac 2 -pc_type lu -pc_factor_mat_solver_type mumps
108: requires: mumps
110: TEST*/