Actual source code: ex2.c

  2: static char help[] = "Tests PC and KSP on a tridiagonal matrix.  Note that most\n\
  3: users should employ the KSP interface instead of using PC directly.\n\n";

 5:  #include petscksp.h
 6:  #include petscpc.h
 7:  #include petsc.h
  8: #include <stdio.h>

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

 25:   PetscInitialize(&argc,&args,(char *)0,help);

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

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

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

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

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

 66:   /* Solve the problem */
 67:   KSPGetType(ksp,&kspname);
 68:   PCGetType(pc,&pcname);
 69:   PetscPrintf(PETSC_COMM_SELF,"Running %s with %s preconditioning\n",kspname,pcname);
 70:   KSPSolve(ksp,b,u);
 71:   VecAXPY(u,-1.0,ustar);
 72:   VecNorm(u,NORM_2,&norm);
 73:   KSPGetIterationNumber(ksp,&its);
 74:   PetscPrintf(PETSC_COMM_SELF,"2 norm of error %A Number of iterations %D\n",norm,its);

 76:   /* Free data structures */
 77:   KSPDestroy(ksp);
 78:   VecDestroy(u);
 79:   VecDestroy(ustar);
 80:   VecDestroy(b);
 81:   MatDestroy(mat);
 82:   PCDestroy(pc);

 84:   PetscFinalize();
 85:   return 0;
 86: }
 87: