Actual source code: ex6.c
2: static char help[] = "Solves a tridiagonal linear system with KSP. \n\
3: It illustrates how to do one symbolic factorization and multiple numeric factorizations using same matrix structure. \n\n";
5: #include <petscksp.h>
6: int main(int argc,char **args)
7: {
8: Vec x, b, u; /* approx solution, RHS, exact solution */
9: Mat A; /* linear system matrix */
10: KSP ksp; /* linear solver context */
11: PC pc; /* preconditioner context */
12: PetscReal norm; /* norm of solution error */
13: PetscInt i,col[3],its,rstart,rend,N=10,num_numfac;
14: PetscScalar value[3];
16: PetscInitialize(&argc,&args,(char*)0,help);
17: PetscOptionsGetInt(NULL,NULL,"-N",&N,NULL);
19: /* Create and assemble matrix. */
20: MatCreate(PETSC_COMM_WORLD,&A);
21: MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);
22: MatSetFromOptions(A);
23: MatSetUp(A);
24: MatGetOwnershipRange(A,&rstart,&rend);
26: value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
27: for (i=rstart; i<rend; i++) {
28: col[0] = i-1; col[1] = i; col[2] = i+1;
29: if (i == 0) {
30: MatSetValues(A,1,&i,2,col+1,value+1,INSERT_VALUES);
31: } else if (i == N-1) {
32: MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
33: } else {
34: MatSetValues(A,1,&i,3,col,value,INSERT_VALUES);
35: }
36: }
37: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
38: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
39: MatSetOption(A,MAT_NEW_NONZERO_LOCATION_ERR,PETSC_TRUE);
41: /* Create vectors */
42: MatCreateVecs(A,&x,&b);
43: VecDuplicate(x,&u);
45: /* Set exact solution; then compute right-hand-side vector. */
46: VecSet(u,1.0);
47: MatMult(A,u,b);
49: /* Create the linear solver and set various options. */
50: KSPCreate(PETSC_COMM_WORLD,&ksp);
51: KSPGetPC(ksp,&pc);
52: PCSetType(pc,PCJACOBI);
53: KSPSetTolerances(ksp,1.e-5,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);
54: KSPSetOperators(ksp,A,A);
55: KSPSetFromOptions(ksp);
57: num_numfac = 1;
58: PetscOptionsGetInt(NULL,NULL,"-num_numfac",&num_numfac,NULL);
59: while (num_numfac--) {
60: /* An example on how to update matrix A for repeated numerical factorization and solve. */
61: PetscScalar one=1.0;
62: PetscInt i = 0;
63: MatSetValues(A,1,&i,1,&i,&one,ADD_VALUES);
64: MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
65: MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
66: /* Update b */
67: MatMult(A,u,b);
69: /* Solve the linear system */
70: KSPSolve(ksp,b,x);
72: /* Check the solution and clean up */
73: VecAXPY(x,-1.0,u);
74: VecNorm(x,NORM_2,&norm);
75: KSPGetIterationNumber(ksp,&its);
76: if (norm > 100*PETSC_MACHINE_EPSILON) {
77: PetscPrintf(PETSC_COMM_WORLD,"Norm of error %g, Iterations %D\n",(double)norm,its);
78: }
79: }
81: /* Free work space. */
82: VecDestroy(&x)); PetscCall(VecDestroy(&u);
83: VecDestroy(&b)); PetscCall(MatDestroy(&A);
84: KSPDestroy(&ksp);
86: PetscFinalize();
87: return 0;
88: }
90: /*TEST
92: test:
93: args: -num_numfac 2 -pc_type lu
95: test:
96: suffix: 2
97: args: -num_numfac 2 -pc_type lu -pc_factor_mat_solver_type mumps
98: requires: mumps
100: test:
101: suffix: 3
102: nsize: 3
103: args: -num_numfac 2 -pc_type lu -pc_factor_mat_solver_type mumps
104: requires: mumps
106: TEST*/