Actual source code: ex2.c

  1: /*$Id: ex2.c,v 1.53 2001/08/07 21:30:37 bsmith Exp $*/

  3: static char help[] = "Tests PC and KSP on a tridiagonal matrix.  Note that mostn
  4: users should employ the SLES interface instead of using PC directly.nn";

 6:  #include petscksp.h
 7:  #include petscpc.h
 8:  #include petsc.h
  9: #include <stdio.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 */
 17:   int         ierr,n = 10,i,its,col[3];
 18:   PetscScalar value[3],mone = -1.0,one = 1.0,zero = 0.0;
 19:   PCType      pcname;
 20:   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(&one,ustar);
 30:   VecSet(&zero,u);

 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:   PCSetVector(pc,u);
 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:   KSPSetSolution(ksp,u);
 62:   KSPSetRhs(ksp,b);
 63:   PCSetOperators(pc,mat,mat,DIFFERENT_NONZERO_PATTERN);
 64:   KSPSetPC(ksp,pc);
 65:   KSPSetUp(ksp);

 67:   /* Solve the problem */
 68:   KSPGetType(ksp,&kspname);
 69:   PCGetType(pc,&pcname);
 70:   PetscPrintf(PETSC_COMM_SELF,"Running %s with %s preconditioningn",kspname,pcname);
 71:   KSPSolve(ksp,&its);
 72:   VecAXPY(&mone,ustar,u);
 73:   VecNorm(u,NORM_2,&norm);
 74:   PetscPrintf(PETSC_COMM_SELF,"2 norm of error %A Number of iterations %dn",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: