DoFs from entities

[ignat...@gmail.com]

Hi all,

I would like to access the DoFs sitting on specific entities in my problem.

Could someone suggest an approach to access them?

Thank you in advance,

Ignatios 

 

[Lukasz Kaczmraczyk]

Hello,

In development version v0.7.16 or later you can find implementation ISManager with isCreateProblemFieldAndRank which allows for getting dofs indices on given entities. 
http://mofem.eng.gla.ac.uk/mofem/html/group__mofem__vectors.html#gae5ec9e148a39f26640926a5cba24ae3a

Here is example how you can use it.

Imagine that you have entities on some surface

Range ents_on_surface;
// get them form sideset/blockset/nodeset

And some discrete manager DM, first we get pointer to the problem in DM,

const MoFEM::Problem *problem_ptr;
CHKERR DMMoFEMGetProblemPtr(dm, &problem_ptr);

Now we like to extract "x" component of displacement filed 

// get is from problem, see MoFEM documentation
IS is;
CHKERR m_field.getInterface<ISManager>()->isCreateProblemFieldAndRank(
  problem_ptr->getName(),ROW,"DISPLACEMENTS",0,1,&is,&ents_on_surface
);
// create vector with is size
int is_size, is_local_size;
CHKERR ISGetSize(is,is_size);
CHKERR ISGetLocalSize(is,is_local_size);
Vec f_with_coeff_0_on_entities;
CHKERR VecCreateMPI(PETSC_COMM_WORLD,is_local_size,is_size,&f_with_coeff_0_on_entities);
// scatter values from f_internal to f_with_coeff_0_on_entities
VecScatter sct;
CHKERR VecScatterCreate(f_internal,is,f_with_coeff_0_on_entities,PETSC_NULL,&sct);
CHKERR VecScatterBegin(sct,f_internal,f_with_coeff_0_on_entities,INSERT_VALUES,SCATTER_FORWARD);
CHKERR VecScatterEnd(sct,f_internal,f_with_coeff_0_on_entities,INSERT_VALUES,SCATTER_FORWARD);
// calculate sum of vector with dofs in x-element on entities
int sum0;
CHKERR VecSum(f_with_coeff_0_on_entities,&sum0);

Kind regards,

Lukasz