Actual source code: ex3.c
petsc-3.8.3 2017-12-09
2: static char help[] = "Demonstrates the use of fast Richardson for SOR. And\n\
3: also tests the MatSOR() routines. Input parameters are:\n\
4: -n <n> : problem dimension\n\n";
6: #include <petscksp.h>
7: #include <petscpc.h>
9: int main(int argc,char **args)
10: {
11: Mat mat; /* matrix */
12: Vec b,ustar,u; /* vectors (RHS, exact solution, approx solution) */
13: PC pc; /* PC context */
14: KSP ksp; /* KSP context */
16: PetscInt n = 10,i,its,col[3];
17: PetscScalar value[3];
18: KSPType kspname;
19: PCType pcname;
21: PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
22: PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
24: /* Create and initialize vectors */
25: VecCreateSeq(PETSC_COMM_SELF,n,&b);
26: VecCreateSeq(PETSC_COMM_SELF,n,&ustar);
27: VecCreateSeq(PETSC_COMM_SELF,n,&u);
28: VecSet(ustar,1.0);
29: VecSet(u,0.0);
31: /* Create and assemble matrix */
32: MatCreateSeqAIJ(PETSC_COMM_SELF,n,n,3,NULL,&mat);
33: value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
34: for (i=1; i<n-1; i++) {
35: col[0] = i-1; col[1] = i; col[2] = i+1;
36: MatSetValues(mat,1,&i,3,col,value,INSERT_VALUES);
37: }
38: i = n - 1; col[0] = n - 2; col[1] = n - 1;
39: MatSetValues(mat,1,&i,2,col,value,INSERT_VALUES);
40: i = 0; col[0] = 0; col[1] = 1; value[0] = 2.0; value[1] = -1.0;
41: MatSetValues(mat,1,&i,2,col,value,INSERT_VALUES);
42: MatAssemblyBegin(mat,MAT_FINAL_ASSEMBLY);
43: MatAssemblyEnd(mat,MAT_FINAL_ASSEMBLY);
45: /* Compute right-hand-side vector */
46: MatMult(mat,ustar,b);
48: /* Create PC context and set up data structures */
49: PCCreate(PETSC_COMM_WORLD,&pc);
50: PCSetType(pc,PCNONE);
51: PCSetFromOptions(pc);
52: PCSetOperators(pc,mat,mat);
53: PCSetUp(pc);
55: /* Create KSP context and set up data structures */
56: KSPCreate(PETSC_COMM_WORLD,&ksp);
57: KSPSetType(ksp,KSPRICHARDSON);
58: KSPSetFromOptions(ksp);
59: PCSetOperators(pc,mat,mat);
60: KSPSetPC(ksp,pc);
61: KSPSetUp(ksp);
63: /* Solve the problem */
64: KSPGetType(ksp,&kspname);
65: PCGetType(pc,&pcname);
66: PetscPrintf(PETSC_COMM_SELF,"Running %s with %s preconditioning\n",kspname,pcname);
67: KSPSolve(ksp,b,u);
68: KSPGetIterationNumber(ksp,&its);
69: PetscPrintf(PETSC_COMM_WORLD,"Number of iterations %D\n",its);
71: /* Free data structures */
72: KSPDestroy(&ksp);
73: VecDestroy(&u);
74: VecDestroy(&ustar);
75: VecDestroy(&b);
76: MatDestroy(&mat);
77: PCDestroy(&pc);
78: PetscFinalize();
79: return ierr;
80: }