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 <stdio.h>

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

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

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

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

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

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

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

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

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

 82:   PetscFinalize();
 83:   return 0;
 84: }
 85: