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>

 11: int main(int argc,char **args)
 12: {
 13:   Mat            mat;          /* matrix */
 14:   Vec            b,ustar,u;  /* vectors (RHS, exact solution, approx solution) */
 15:   PC             pc;           /* PC context */
 16:   KSP            ksp;          /* KSP context */
 18:   PetscInt       n = 10,i,its,col[3];
 19:   PetscScalar    value[3];
 20:   KSPType        kspname;
 21:   PCType         pcname;

 23:   PetscInitialize(&argc,&args,(char*)0,help);
 24:   PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);

 26:   /* Create and initialize vectors */
 27:   VecCreateSeq(PETSC_COMM_SELF,n,&b);
 28:   VecCreateSeq(PETSC_COMM_SELF,n,&ustar);
 29:   VecCreateSeq(PETSC_COMM_SELF,n,&u);
 30:   VecSet(ustar,1.0);
 31:   VecSet(u,0.0);

 33:   /* Create and assemble matrix */
 34:   MatCreateSeqAIJ(PETSC_COMM_SELF,n,n,3,NULL,&mat);
 35:   value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
 36:   for (i=1; i<n-1; i++) {
 37:     col[0] = i-1; col[1] = i; col[2] = i+1;
 38:     MatSetValues(mat,1,&i,3,col,value,INSERT_VALUES);
 39:   }
 40:   i    = n - 1; col[0] = n - 2; col[1] = n - 1;
 41:   MatSetValues(mat,1,&i,2,col,value,INSERT_VALUES);
 42:   i    = 0; col[0] = 0; col[1] = 1; value[0] = 2.0; value[1] = -1.0;
 43:   MatSetValues(mat,1,&i,2,col,value,INSERT_VALUES);
 44:   MatAssemblyBegin(mat,MAT_FINAL_ASSEMBLY);
 45:   MatAssemblyEnd(mat,MAT_FINAL_ASSEMBLY);

 47:   /* Compute right-hand-side vector */
 48:   MatMult(mat,ustar,b);

 50:   /* Create PC context and set up data structures */
 51:   PCCreate(PETSC_COMM_WORLD,&pc);
 52:   PCSetType(pc,PCNONE);
 53:   PCSetFromOptions(pc);
 54:   PCSetOperators(pc,mat,mat);
 55:   PCSetUp(pc);

 57:   /* Create KSP context and set up data structures */
 58:   KSPCreate(PETSC_COMM_WORLD,&ksp);
 59:   KSPSetType(ksp,KSPRICHARDSON);
 60:   KSPSetFromOptions(ksp);
 61:   PCSetOperators(pc,mat,mat);
 62:   KSPSetPC(ksp,pc);
 63:   KSPSetUp(ksp);

 65:   /* Solve the problem */
 66:   KSPGetType(ksp,&kspname);
 67:   PCGetType(pc,&pcname);
 68:   PetscPrintf(PETSC_COMM_SELF,"Running %s with %s preconditioning\n",kspname,pcname);
 69:   KSPSolve(ksp,b,u);
 70:   KSPGetIterationNumber(ksp,&its);
 71:   PetscPrintf(PETSC_COMM_WORLD,"Number of iterations %D\n",its);

 73:   /* Free data structures */
 74:   KSPDestroy(&ksp);
 75:   VecDestroy(&u);
 76:   VecDestroy(&ustar);
 77:   VecDestroy(&b);
 78:   MatDestroy(&mat);
 79:   PCDestroy(&pc);
 80:   PetscFinalize();
 81:   return 0;
 82: }