Actual source code: ex24.c
2: static char help[] = "Tests CG, MINRES and SYMMLQ on symmetric matrices with SBAIJ format. The preconditioner ICC only works on sequential SBAIJ format. \n\n";
4: #include petscksp.h
9: int main(int argc,char **args)
10: {
11: Mat C;
12: PetscScalar v,none = -1.0;
13: PetscInt i,j,Ii,J,Istart,Iend,N,m = 4,n = 4,its,k;
15: PetscMPIInt size,rank;
16: PetscReal err_norm,res_norm;
17: Vec x,b,u,u_tmp;
18: PetscRandom r;
19: PC pc;
20: KSP ksp;
22: PetscInitialize(&argc,&args,(char *)0,help);
23: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
24: MPI_Comm_size(PETSC_COMM_WORLD,&size);
25: PetscOptionsGetInt(PETSC_NULL,"-m",&m,PETSC_NULL);
26: PetscOptionsGetInt(PETSC_NULL,"-n",&n,PETSC_NULL);
27: N = m*n;
30: /* Generate matrix */
31: MatCreate(PETSC_COMM_WORLD,&C);
32: MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,N,N);
33: MatSetFromOptions(C);
34: MatGetOwnershipRange(C,&Istart,&Iend);
35: for (Ii=Istart; Ii<Iend; Ii++) {
36: v = -1.0; i = Ii/n; j = Ii - i*n;
37: if (i>0) {J = Ii - n; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
38: if (i<m-1) {J = Ii + n; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
39: if (j>0) {J = Ii - 1; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
40: if (j<n-1) {J = Ii + 1; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
41: v = 4.0; MatSetValues(C,1,&Ii,1,&Ii,&v,ADD_VALUES);
42: }
43: MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
44: MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
46: /* a shift can make C indefinite. Preconditioners LU, ILU (for BAIJ format) and ICC may fail */
47: /* MatShift(C,alpha); */
48: /* MatView(C,PETSC_VIEWER_STDOUT_WORLD); */
50: /* Setup and solve for system */
51: /* Create vectors. */
52: VecCreate(PETSC_COMM_WORLD,&x);
53: VecSetSizes(x,PETSC_DECIDE,N);
54: VecSetFromOptions(x);
55: VecDuplicate(x,&b);
56: VecDuplicate(x,&u);
57: VecDuplicate(x,&u_tmp);
58: /* Set exact solution u; then compute right-hand-side vector b. */
59: PetscRandomCreate(PETSC_COMM_SELF,&r);
60: PetscRandomSetFromOptions(r);
61: VecSetRandom(u,r);
62: PetscRandomDestroy(r);
63: MatMult(C,u,b);
65: for (k=0; k<3; k++){
66: if (k == 0){ /* CG */
67: KSPCreate(PETSC_COMM_WORLD,&ksp);
68: KSPSetOperators(ksp,C,C,DIFFERENT_NONZERO_PATTERN);
69: PetscPrintf(PETSC_COMM_WORLD,"\n CG: \n");
70: KSPSetType(ksp,KSPCG);
71: } else if (k == 1){ /* MINRES */
72: KSPCreate(PETSC_COMM_WORLD,&ksp);
73: KSPSetOperators(ksp,C,C,DIFFERENT_NONZERO_PATTERN);
74: PetscPrintf(PETSC_COMM_WORLD,"\n MINRES: \n");
75: KSPSetType(ksp,KSPMINRES);
76: } else { /* SYMMLQ */
77: KSPCreate(PETSC_COMM_WORLD,&ksp);
78: KSPSetOperators(ksp,C,C,DIFFERENT_NONZERO_PATTERN);
79: PetscPrintf(PETSC_COMM_WORLD,"\n SYMMLQ: \n");
80: KSPSetType(ksp,KSPSYMMLQ);
81: }
82: KSPGetPC(ksp,&pc);
83: /* PCSetType(pc,PCICC); */
84: PCSetType(pc,PCJACOBI);
85: KSPSetTolerances(ksp,1.e-7,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);
87: /*
88: Set runtime options, e.g.,
89: -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
90: These options will override those specified above as long as
91: KSPSetFromOptions() is called _after_ any other customization
92: routines.
93: */
94: KSPSetFromOptions(ksp);
96: /* Solve linear system; */
97: KSPSetUp(ksp);
98: KSPSolve(ksp,b,x);
100: KSPGetIterationNumber(ksp,&its);
101: /* Check error */
102: VecCopy(u,u_tmp);
103: VecAXPY(u_tmp,none,x);
104: VecNorm(u_tmp,NORM_2,&err_norm);
105: MatMult(C,x,u_tmp);
106: VecAXPY(u_tmp,none,b);
107: VecNorm(u_tmp,NORM_2,&res_norm);
108:
109: PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
110: PetscPrintf(PETSC_COMM_WORLD,"Residual norm %A;",res_norm);
111: PetscPrintf(PETSC_COMM_WORLD," Error norm %A.\n",err_norm);
113: KSPDestroy(ksp);
114: }
115:
116: /*
117: Free work space. All PETSc objects should be destroyed when they
118: are no longer needed.
119: */
120: VecDestroy(b);
121: VecDestroy(u);
122: VecDestroy(x);
123: VecDestroy(u_tmp);
124: MatDestroy(C);
126: PetscFinalize();
127: return 0;
128: }