Actual source code: ex24.c

petsc-3.7.3 2016-07-24
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  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:   PC             pc;
 19:   KSP            ksp;

 21:   PetscInitialize(&argc,&args,(char*)0,help);
 22:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
 23:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 24:   PetscOptionsGetInt(NULL,NULL,"-m",&m,NULL);
 25:   PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
 26:   N    = m*n;


 29:   /* Generate matrix */
 30:   MatCreate(PETSC_COMM_WORLD,&C);
 31:   MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,N,N);
 32:   MatSetFromOptions(C);
 33:   MatSetUp(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:   VecSet(u,1.0);
 60:   MatMult(C,u,b);

 62:   for (k=0; k<3; k++) {
 63:     if (k == 0) {                              /* CG  */
 64:       KSPCreate(PETSC_COMM_WORLD,&ksp);
 65:       KSPSetOperators(ksp,C,C);
 66:       PetscPrintf(PETSC_COMM_WORLD,"\n CG: \n");
 67:       KSPSetType(ksp,KSPCG);
 68:     } else if (k == 1) {                       /* MINRES */
 69:       KSPCreate(PETSC_COMM_WORLD,&ksp);
 70:       KSPSetOperators(ksp,C,C);
 71:       PetscPrintf(PETSC_COMM_WORLD,"\n MINRES: \n");
 72:       KSPSetType(ksp,KSPMINRES);
 73:     } else {                                 /* SYMMLQ */
 74:       KSPCreate(PETSC_COMM_WORLD,&ksp);
 75:       KSPSetOperators(ksp,C,C);
 76:       PetscPrintf(PETSC_COMM_WORLD,"\n SYMMLQ: \n");
 77:       KSPSetType(ksp,KSPSYMMLQ);
 78:     }
 79:     KSPGetPC(ksp,&pc);
 80:     /* PCSetType(pc,PCICC); */
 81:     PCSetType(pc,PCJACOBI);
 82:     KSPSetTolerances(ksp,1.e-7,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);

 84:     /*
 85:     Set runtime options, e.g.,
 86:         -ksp_type <type> -pc_type <type> -ksp_monitor -ksp_rtol <rtol>
 87:     These options will override those specified above as long as
 88:     KSPSetFromOptions() is called _after_ any other customization
 89:     routines.
 90:     */
 91:     KSPSetFromOptions(ksp);

 93:     /* Solve linear system; */
 94:     KSPSetUp(ksp);
 95:     KSPSolve(ksp,b,x);

 97:     KSPGetIterationNumber(ksp,&its);
 98:     /* Check error */
 99:     VecCopy(u,u_tmp);
100:     VecAXPY(u_tmp,none,x);
101:     VecNorm(u_tmp,NORM_2,&err_norm);
102:     MatMult(C,x,u_tmp);
103:     VecAXPY(u_tmp,none,b);
104:     VecNorm(u_tmp,NORM_2,&res_norm);

106:     PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
107:     PetscPrintf(PETSC_COMM_WORLD,"Residual norm %g;",(double)res_norm);
108:     PetscPrintf(PETSC_COMM_WORLD,"  Error norm %g.\n",(double)err_norm);
109:     KSPDestroy(&ksp);
110:   }

112:   /*
113:        Free work space.  All PETSc objects should be destroyed when they
114:        are no longer needed.
115:   */
116:   VecDestroy(&b);
117:   VecDestroy(&u);
118:   VecDestroy(&x);
119:   VecDestroy(&u_tmp);
120:   MatDestroy(&C);

122:   PetscFinalize();
123:   return 0;
124: }