Reference documentation for deal.II version 9.5.0

#include <deal.II/numerics/solution_transfer.h>
Classes  
struct  Pointerstruct 
Public Member Functions  
SolutionTransfer (const DoFHandler< dim, spacedim > &dof)  
~SolutionTransfer ()  
void  clear () 
void  prepare_for_pure_refinement () 
void  prepare_for_coarsening_and_refinement (const std::vector< VectorType > &all_in) 
void  prepare_for_coarsening_and_refinement (const VectorType &in) 
void  refine_interpolate (const VectorType &in, VectorType &out) const 
void  interpolate (const std::vector< VectorType > &all_in, std::vector< VectorType > &all_out) const 
void  interpolate (const VectorType &in, VectorType &out) const 
std::size_t  memory_consumption () const 
Static Public Member Functions  
static ::ExceptionBase &  ExcNotPrepared () 
static ::ExceptionBase &  ExcAlreadyPrepForRef () 
static ::ExceptionBase &  ExcAlreadyPrepForCoarseAndRef () 
Private Types  
enum  PreparationState { none , pure_refinement , coarsening_and_refinement } 
Private Attributes  
SmartPointer< const DoFHandler< dim, spacedim >, SolutionTransfer< dim, VectorType, spacedim > >  dof_handler 
types::global_dof_index  n_dofs_old 
PreparationState  prepared_for 
std::vector< std::vector< types::global_dof_index > >  indices_on_cell 
std::map< std::pair< unsigned int, unsigned int >, Pointerstruct >  cell_map 
std::vector< std::vector< Vector< typename VectorType::value_type > > >  dof_values_on_cell 
This class implements the transfer of a discrete FE function (e.g. a solution vector) from one mesh to another that is obtained from the first by a single refinement and/or coarsening step. During interpolation the vector is reinitialized to the new size and filled with the interpolated values. This class is used in the step15, step26, step31, and step33 tutorial programs. A version of this class that works on parallel triangulations is available as parallel::distributed::SolutionTransfer.
This class implements the algorithms in two different ways:
If the grid will only be refined (i.e. no cells are coarsened) then use SolutionTransfer
as follows:
Then to proceed do
Although the refine_interpolate
functions are allowed to be called multiple times, e.g. for interpolating several solution vectors, there is the following possibility of interpolating several functions simultaneously.
This is used in several of the tutorial programs, for example step31.
If the grid has cells that will be coarsened, then use SolutionTransfer
as follows:
If the grid is partitioned across several MPI processes, then it is important to note that the old solution(s) must be copied to one that also provides access to the locally relevant DoF values (these values required for the interpolation process):
Multiple calls to the function interpolate (const VectorType &in, VectorType &out)
are NOT allowed. Interpolating several functions can be performed in one step by using void interpolate (const vector<VectorType> &all_in, vector<VectorType> &all_out) const
, and using the respective prepare_for_coarsening_and_refinement
function taking several vectors as input before actually refining and coarsening the triangulation (see there).
For deleting all stored data in SolutionTransfer
and reinitializing it use the clear()
function.
The template argument VectorType
denotes the type of data container you want to transfer.
The interpolation onto the new mesh is a local operation, i.e., it interpolates onto the new mesh only. If that new mesh has hanging nodes, you will therefore get a solution that does not satisfy hanging node constraints. The same is true with boundary values: the interpolated solution will just be the interpolation of the old solution at the boundary, and this may or may not satisfy boundary values at newly introduced boundary nodes.
Consequently, you may have to apply hanging node or boundary value constraints after interpolation. step15 and step26 have examples of dealing with this.
Solution transfer with only refinement. Assume that we have got a solution vector on the current (original) grid. Each entry of this vector belongs to one of the DoFs of the discretization. If we now refine the grid then the calling of DoFHandler::distribute_dofs() will change at least some of the DoF indices. Hence we need to store the DoF indices of all active cells before the refinement. A pointer for each active cell is used to point to the vector of these DoF indices of that cell. This is done by prepare_for_pure_refinement().
In the function refine_interpolate(in,out)
and on each cell where the pointer is set (i.e. the cells that were active in the original grid) we can now access the local values of the solution vector in
on that cell by using the stored DoF indices. These local values are interpolated and set into the vector out
that is at the end the discrete function in
interpolated on the refined mesh.
The refine_interpolate(in,out)
function can be called multiple times for arbitrary many discrete functions (solution vectors) on the original grid.
Solution transfer with coarsening and refinement. After calling Triangulation::prepare_coarsening_and_refinement the coarsen flags of either all or none of the children of a (father)cell are set. While coarsening (Triangulation::execute_coarsening_and_refinement) the cells that are not needed any more will be deleted from the Triangulation.
For the interpolation from the (to be coarsenend) children to their father the children cells are needed. Hence this interpolation and the storing of the interpolated values of each of the discrete functions that we want to interpolate needs to take place before these children cells are coarsened (and deleted!!). Again a pointer for each relevant cell is set to point to these values (see below). Additionally the DoF indices of the cells that will not be coarsened need to be stored according to the solution transfer with pure refinement (cf there). All this is performed by prepare_for_coarsening_and_refinement(all_in)
where the vector<VectorType> all_in
includes all discrete functions to be interpolated onto the new grid.
As we need two different kinds of pointers (vector<unsigned int> *
for the Dof indices and vector<VectorType> *
for the interpolated DoF values) we use the Pointerstruct
that includes both of these pointers and the pointer for each cell points to these Pointerstructs
. On each cell only one of the two different pointers is used at one time hence we could use a void * pointer
as vector<unsigned int> *
at one time and as vector<VectorType> *
at the other but using this Pointerstruct
in between makes the use of these pointers more safe and gives better possibility to expand their usage.
In interpolate(all_in, all_out)
the refined cells are treated according to the solution transfer while pure refinement. Additionally, on each cell that is coarsened (hence previously was a father cell), the values of the discrete functions in all_out
are set to the stored local interpolated values that are accessible due to the 'vector<VectorType> *' pointer in Pointerstruct
that is pointed to by the pointer of that cell. It is clear that interpolate(all_in, all_out)
only can be called with the vector<VectorType> all_in
that previously was the parameter of the prepare_for_coarsening_and_refinement(all_in)
function. Hence interpolate(all_in, all_out)
can (in contrast to refine_interpolate(in, out)
) only be called once.
This class does its best to represent on the new mesh the finite element function that existed on the old mesh, but this may lead to situations where the function on the new mesh is no longer conforming at hanging nodes. To this end, consider a situation of a twice refined mesh that started with a single square cell (i.e., we now have 16 cells). Consider also that we coarsen 4 of the cells back to the first refinement level. In this case, we end up with a mesh that will look as follows if we were to use a \(Q_1\) element:
The process of interpolating from the old to the new mesh would imply that the values of the finite element function will not change on all of the cells that remained as they are (i.e., the fine cells) but that on the coarse cell at the top right, the four values at the vertices are obtained by interpolating down from its former children. If the original function was not linear, this implies that the marked hanging nodes will retain their old values which, in general, will not lead to a continuous function along the corresponding edges. In other words, the solution vector obtained after SolutionTransfer::interpolate() does not satisfy hanging node constraints: it corresponds to the pointwise interpolation, but not to the interpolation onto the new finite element space that contains constraints from hanging nodes.
Whether this is a problem you need to worry about or not depends on your application. The situation is easily corrected, of course, by applying AffineConstraints::distribute() to your solution vector after transfer, using a constraints object computed on the new DoFHandler object (you probably need to create this object anyway if you have hanging nodes). This is also what is done, for example, in step15.
In the case of DoFHandlers with hpcapabilities, nothing defines which of the finite elements that are part of the hp::FECollection associated with the DoFHandler, should be considered on cells that are not active (i.e., that have children). This is because degrees of freedom are only allocated for active cells and, in fact, it is not allowed to set an active FE index on nonactive cells using DoFAccessor::set_active_fe_index().
It is, thus, not entirely natural what should happen if, for example, a few cells are coarsened away. This class then implements the following algorithm:
Definition at line 336 of file solution_transfer.h.

private 
Declaration of PreparationState
that denotes the three possible states of the SolutionTransfer:
being prepared for 'pure refinement', prepared for 'coarsening and refinement' or not prepared.
Enumerator  

none  The SolutionTransfer is not yet prepared. 
pure_refinement  The SolutionTransfer is prepared for purely refinement. 
coarsening_and_refinement  The SolutionTransfer is prepared for coarsening and refinement. 
Definition at line 485 of file solution_transfer.h.
SolutionTransfer< dim, VectorType, spacedim >::SolutionTransfer  (  const DoFHandler< dim, spacedim > &  dof  ) 
Constructor, takes the current DoFHandler as argument.
Definition at line 46 of file solution_transfer.cc.
SolutionTransfer< dim, VectorType, spacedim >::~SolutionTransfer 
Destructor
Definition at line 65 of file solution_transfer.cc.
void SolutionTransfer< dim, VectorType, spacedim >::clear 
Reinit this class to the state that it has directly after calling the Constructor
Definition at line 74 of file solution_transfer.cc.
void SolutionTransfer< dim, VectorType, spacedim >::prepare_for_pure_refinement 
Prepares the SolutionTransfer
for pure refinement. It stores the dof indices of each cell. After calling this function only calling the refine_interpolate
functions is allowed.
Definition at line 87 of file solution_transfer.cc.
void SolutionTransfer< dim, VectorType, spacedim >::prepare_for_coarsening_and_refinement  (  const std::vector< VectorType > &  all_in  ) 
Prepares the SolutionTransfer
for coarsening and refinement. It stores the dof indices of each cell and stores the dof values of the vectors in all_in
in each cell that'll be coarsened. all_in
includes all vectors that are to be interpolated onto the new (refined and/or coarsenend) grid.
Definition at line 280 of file solution_transfer.cc.
void SolutionTransfer< dim, VectorType, spacedim >::prepare_for_coarsening_and_refinement  (  const VectorType &  in  ) 
Same as previous function but for only one discrete function to be interpolated.
Definition at line 436 of file solution_transfer.cc.
void SolutionTransfer< dim, VectorType, spacedim >::refine_interpolate  (  const VectorType &  in, 
VectorType &  out  
)  const 
This function interpolates the discrete function in
, which is a vector on the grid before the refinement, to the function out
which then is a vector on the refined grid. It assumes the vectors having the right sizes (i.e. in.size()==n_dofs_old
, out.size()==n_dofs_refined
)
Calling this function is allowed only if prepare_for_pure_refinement
is called and the refinement is executed before. Multiple calling of this function is allowed. e.g. for interpolating several functions.
Definition at line 136 of file solution_transfer.cc.
void SolutionTransfer< dim, VectorType, spacedim >::interpolate  (  const std::vector< VectorType > &  all_in, 
std::vector< VectorType > &  all_out  
)  const 
This function interpolates the discrete functions that are stored in all_in
onto the refined and/or coarsenend grid. It assumes the vectors in all_in
denote the same vectors as in all_in
as parameter of prepare_for_refinement_and_coarsening(all_in)
. However, there is no way of verifying this internally, so be careful here.
Calling this function is allowed only if first Triangulation::prepare_coarsening_and_refinement, second SolutionTransfer::prepare_for_coarsening_and_refinement
, an then third Triangulation::execute_coarsening_and_refinement are called before. Multiple calling of this function is NOT allowed. Interpolating several functions can be performed in one step.
The number of output vectors is assumed to be the same as the number of input vectors. Also, the sizes of the output vectors are assumed to be of the right size (n_dofs_refined
). Otherwise an assertion will be thrown.
Definition at line 447 of file solution_transfer.cc.
void SolutionTransfer< dim, VectorType, spacedim >::interpolate  (  const VectorType &  in, 
VectorType &  out  
)  const 
Same as the previous function. It interpolates only one function. It assumes the vectors having the right sizes (i.e. in.size()==n_dofs_old
, out.size()==n_dofs_refined
)
Multiple calling of this function is NOT allowed. Interpolating several functions can be performed in one step by using interpolate (all_in, all_out)
Definition at line 592 of file solution_transfer.cc.
std::size_t SolutionTransfer< dim, VectorType, spacedim >::memory_consumption 
Determine an estimate for the memory consumption (in bytes) of this object.
Definition at line 611 of file solution_transfer.cc.

private 
Pointer to the degree of freedom handler to work with.
Definition at line 473 of file solution_transfer.h.

private 
Stores the number of DoFs before the refinement and/or coarsening.
Definition at line 478 of file solution_transfer.h.

private 
Definition of the respective variable.
Definition at line 504 of file solution_transfer.h.

private 
Is used for prepare_for_refining
(of course also for repare_for_refining_and_coarsening
) and stores all dof indices of the cells that'll be refined
Definition at line 512 of file solution_transfer.h.

private 
Map mapping from level and index of cell to the Pointerstructs
(cf. there). This map makes it possible to keep all the information needed to transfer the solution inside this object rather than using user pointers of the Triangulation for this purpose.
Definition at line 559 of file solution_transfer.h.

private 
Is used for prepare_for_refining_and_coarsening
The interpolated dof values of all cells that'll be coarsened will be stored in this vector.
Definition at line 566 of file solution_transfer.h.