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,I,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,PETSC_DECIDE,PETSC_DECIDE,N,N,&C);
32: MatSetFromOptions(C);
33: MatGetOwnershipRange(C,&Istart,&Iend);
34: for (I=Istart; I<Iend; I++) {
35: v = -1.0; i = I/n; j = I - i*n;
36: if (i>0) {J = I - n; MatSetValues(C,1,&I,1,&J,&v,ADD_VALUES);}
37: if (i<m-1) {J = I + n; MatSetValues(C,1,&I,1,&J,&v,ADD_VALUES);}
38: if (j>0) {J = I - 1; MatSetValues(C,1,&I,1,&J,&v,ADD_VALUES);}
39: if (j<n-1) {J = I + 1; MatSetValues(C,1,&I,1,&J,&v,ADD_VALUES);}
40: v = 4.0; MatSetValues(C,1,&I,1,&I,&v,ADD_VALUES);
41: }
42: MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
43: MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
45: /* a shift can make C indefinite. Preconditioners LU, ILU (for BAIJ format) and ICC may fail */
46: /* MatShift(&alpha, C); */
47: /* MatView(C,PETSC_VIEWER_STDOUT_WORLD); */
49: /* Setup and solve for system */
50:
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);
59: /* Set exact solution u; then compute right-hand-side vector b. */
60: PetscRandomCreate(PETSC_COMM_SELF,RANDOM_DEFAULT,&r);
61: VecSetRandom(r,u);
62: PetscRandomDestroy(r);
63:
64: MatMult(C,u,b);
66: for (k=0; k<3; k++){
67: if (k == 0){ /* CG */
68: KSPCreate(PETSC_COMM_WORLD,&ksp);
69: KSPSetOperators(ksp,C,C,DIFFERENT_NONZERO_PATTERN);
70: PetscPrintf(PETSC_COMM_WORLD,"\n CG: \n");
71: KSPSetType(ksp,KSPCG);
72: } else if (k == 1){ /* MINRES */
73: KSPCreate(PETSC_COMM_WORLD,&ksp);
74: KSPSetOperators(ksp,C,C,DIFFERENT_NONZERO_PATTERN);
75: PetscPrintf(PETSC_COMM_WORLD,"\n MINRES: \n");
76: KSPSetType(ksp,KSPMINRES);
77: } else { /* SYMMLQ */
78: KSPCreate(PETSC_COMM_WORLD,&ksp);
79: KSPSetOperators(ksp,C,C,DIFFERENT_NONZERO_PATTERN);
80: PetscPrintf(PETSC_COMM_WORLD,"\n SYMMLQ: \n");
81: KSPSetType(ksp,KSPSYMMLQ);
82: }
84: KSPGetPC(ksp,&pc);
85: /* PCSetType(pc,PCICC); */
86: PCSetType(pc,PCJACOBI);
87: KSPSetTolerances(ksp,1.e-7,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);
89: /*
90: Set runtime options, e.g.,
91: -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
92: These options will override those specified above as long as
93: KSPSetFromOptions() is called _after_ any other customization
94: routines.
95: */
96: KSPSetFromOptions(ksp);
98: /* Solve linear system; */
99: KSPSolve(ksp,b,x);
101: KSPGetIterationNumber(ksp,&its);
102: /* Check error */
103: VecCopy(u,u_tmp);
104: VecAXPY(&none,x,u_tmp);
105: VecNorm(u_tmp,NORM_2,&err_norm);
106: MatMult(C,x,u_tmp);
107: VecAXPY(&none,b,u_tmp);
108: VecNorm(u_tmp,NORM_2,&res_norm);
109:
110: PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
111: PetscPrintf(PETSC_COMM_WORLD,"Residual norm %A;",res_norm);
112: PetscPrintf(PETSC_COMM_WORLD," Error norm %A.\n",err_norm);
114: KSPDestroy(ksp);
115: }
116:
117: /*
118: Free work space. All PETSc objects should be destroyed when they
119: are no longer needed.
120: */
121: VecDestroy(b);
122: VecDestroy(u);
123: VecDestroy(x);
124: VecDestroy(u_tmp);
125: MatDestroy(C);
127: PetscFinalize();
128: return 0;
129: }