Actual source code: ex44.c

petsc-3.12.2 2019-11-22
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  2: static char help[] = "Solves a tridiagonal linear system.  Designed to compare SOR for different Mat impls.\n\n";

  4:  #include <petscksp.h>

  6: int main(int argc,char **args)
  7: {
  8:   KSP            ksp;      /* linear solver context */
  9:   Mat            A;        /* linear system matrix */
 10:   Vec            x,b;      /* approx solution, RHS */
 11:   PetscInt       Ii,Istart,Iend;
 13:   PetscScalar    v[3] = {-1./2., 1., -1./2.};
 14:   PetscInt       j[3];
 15:   PetscInt       k=15;
 16:   PetscInt       M,m=420;

 18:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 19:   PetscOptionsGetInt(NULL,NULL,"-k",&k,NULL);
 20:   PetscOptionsGetInt(NULL,NULL,"-m",&m,NULL);

 22:   KSPCreate(PETSC_COMM_WORLD,&ksp);
 23:   KSPSetFromOptions(ksp);
 24:   KSPGetOperators(ksp,&A,NULL);

 26:   MatSetSizes(A,m,m,PETSC_DETERMINE,PETSC_DETERMINE);
 27:   MatSetFromOptions(A);
 28:   MatSetUp(A);
 29:   MatGetOwnershipRange(A,&Istart,&Iend);
 30:   MatGetSize(A,&M,NULL);
 31:   for (Ii=Istart; Ii<Iend; Ii++) {
 32:     j[0] = Ii - k;
 33:     j[1] = Ii;
 34:     j[2] = (Ii + k) < M ? (Ii + k) : -1;
 35:     MatSetValues(A,1,&Ii,3,j,v,INSERT_VALUES);
 36:   }
 37:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 38:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
 39:   MatCreateVecs(A,&x,&b);

 41:   VecSetFromOptions(b);
 42:   VecSet(b,1.0);
 43:   VecSetFromOptions(x);
 44:   VecSet(x,2.0);

 46:   KSPSolve(ksp,b,x);

 48:   VecDestroy(&b);
 49:   VecDestroy(&x);
 50:   KSPDestroy(&ksp);

 52:   PetscFinalize();
 53:   return ierr;
 54: }