Actual source code: ex24.c
petsc-3.6.4 2016-04-12
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,err_tol=1.e-7,res_tol=1.e-6;
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(NULL,"-m",&m,NULL);
26: PetscOptionsGetInt(NULL,"-n",&n,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: MatSetUp(C);
35: MatGetOwnershipRange(C,&Istart,&Iend);
36: for (Ii=Istart; Ii<Iend; Ii++) {
37: v = -1.0; i = Ii/n; j = Ii - i*n;
38: if (i>0) {J = Ii - n; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
39: if (i<m-1) {J = Ii + n; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
40: if (j>0) {J = Ii - 1; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
41: if (j<n-1) {J = Ii + 1; MatSetValues(C,1,&Ii,1,&J,&v,ADD_VALUES);}
42: v = 4.0; MatSetValues(C,1,&Ii,1,&Ii,&v,ADD_VALUES);
43: }
44: MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
45: MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
47: /* a shift can make C indefinite. Preconditioners LU, ILU (for BAIJ format) and ICC may fail */
48: /* MatShift(C,alpha); */
49: /* MatView(C,PETSC_VIEWER_STDOUT_WORLD); */
51: /* Setup and solve for system */
52: /* Create vectors. */
53: VecCreate(PETSC_COMM_WORLD,&x);
54: VecSetSizes(x,PETSC_DECIDE,N);
55: VecSetFromOptions(x);
56: VecDuplicate(x,&b);
57: VecDuplicate(x,&u);
58: VecDuplicate(x,&u_tmp);
59: /* Set exact solution u; then compute right-hand-side vector b. */
60: PetscRandomCreate(PETSC_COMM_SELF,&r);
61: PetscRandomSetFromOptions(r);
62: VecSetRandom(u,r);
63: PetscRandomDestroy(&r);
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);
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);
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);
80: PetscPrintf(PETSC_COMM_WORLD,"\n SYMMLQ: \n");
81: KSPSetType(ksp,KSPSYMMLQ);
82: }
83: KSPGetPC(ksp,&pc);
84: /* PCSetType(pc,PCICC); */
85: PCSetType(pc,PCJACOBI);
86: KSPSetTolerances(ksp,1.e-7,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);
88: /*
89: Set runtime options, e.g.,
90: -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
91: These options will override those specified above as long as
92: KSPSetFromOptions() is called _after_ any other customization
93: routines.
94: */
95: KSPSetFromOptions(ksp);
97: /* Solve linear system; */
98: KSPSetUp(ksp);
99: KSPSolve(ksp,b,x);
101: KSPGetIterationNumber(ksp,&its);
102: /* Check error */
103: VecCopy(u,u_tmp);
104: VecAXPY(u_tmp,none,x);
105: VecNorm(u_tmp,NORM_2,&err_norm);
106: MatMult(C,x,u_tmp);
107: VecAXPY(u_tmp,none,b);
108: VecNorm(u_tmp,NORM_2,&res_norm);
110: PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
111: if (res_norm > res_tol) {
112: PetscPrintf(PETSC_COMM_WORLD,"Residual norm %g;",(double)res_norm);
113: }
114: if (err_norm > err_tol) {
115: PetscPrintf(PETSC_COMM_WORLD," Error norm %g.\n",(double)err_norm);
116: }
117: KSPDestroy(&ksp);
118: }
120: /*
121: Free work space. All PETSc objects should be destroyed when they
122: are no longer needed.
123: */
124: VecDestroy(&b);
125: VecDestroy(&u);
126: VecDestroy(&x);
127: VecDestroy(&u_tmp);
128: MatDestroy(&C);
130: PetscFinalize();
131: return 0;
132: }