[petsc-users] coordinates of vertices of a cell in 3D DMPlex

[Mark Adams]

Oh, here is a way to get an elements coordinates from the coordinate vector:

DM                plex;
ierr = DMConvert(dm, DMPLEX, &plex);CHKERRQ(ierr);
PetscSection      section,globsection;
ierr = DMGetLocalSection(plex, &section);CHKERRQ(ierr);
ierr = DMPlexVecGetClosure(plex, section, crd_vec, cell, NULL,
&coef);CHKERRQ(ierr);
....
ierr = DMPlexVecRestoreClosure(plex, section, crd_vec, cell, NULL,
&coef);CHKERRQ(ierr);

On Sat, Jul 25, 2020 at 7:13 AM Mark Adams <mfadams at lbl.gov> wrote:

> I get all the coordinates with this method:
>
> static PetscErrorCode crd_func(PetscInt dim, PetscReal time, const
> PetscReal x[], PetscInt Nf_dummy, PetscScalar *u, void *actx)
> {
>   int i;
>   PetscFunctionBeginUser;
>   for (i = 0; i < dim; ++i) u[i] = x[i];
>   PetscFunctionReturn(0);
> }
>
>   PetscErrorCode (*initu[1])(PetscInt, PetscReal, const PetscReal [],
> PetscInt, PetscScalar [], void *);
>   /* project coordinates to vertices */
>   ierr = DMCreateGlobalVector(crddm, &crd_vec);CHKERRV(ierr);
>   initu[0] = crd_func;
>   ierr = DMProjectFunction(crddm, 0.0, initu, NULL, INSERT_ALL_VALUES,
> crd_vec);CHKERRV(ierr);
>   ierr = VecViewFromOptions(crd_vec, NULL, "-coord_view");CHKERRV(ierr);
>   /* iterate over mesh data and get indices */
>   ierr = VecGetArrayRead(crd_vec,&xx);CHKERRV(ierr);
>   ierr = VecGetLocalSize(rho,&N);CHKERRV(ierr);
>   /* access grid data here */
>   for (p=0;p<N;p++) {
>     for (i=0;i<dim;i++) ..... = xx[p*dim+i];
>     PetscPrintf(PETSC_COMM_SELF,"xx = (%g, %g)\n", xx[p*dim+0],
> xx[p*dim+1]);
>   }
>   ierr = VecRestoreArrayRead(crd_vec,&xx);CHKERRV(ierr);
>   ierr = VecDestroy(&crd_vec);CHKERRV(ierr);
>
> On Sat, Jul 25, 2020 at 4:10 AM Swarnava Ghosh <swarnava89 at gmail.com>
> wrote:
>
>> Dear Petsc users,
>>
>> I had a trivial question about DMPlex. Suppose I have a 3D mesh of
>> tetrahedrons. I want to find out the 3D coordinates of the vertices of a
>> particular cell. What would be the function to do this?
>>
>> Thank you,
>> SG
>>
>
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