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

[Stefano Zampini]

Mark

This will only work if you have a vector space for the function


> On Jul 25, 2020, at 1:13 PM, 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 <mailto: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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