void SelectSubsetElements(ISelector& sel, ISubsetHandler& sh, int subsetIndex,
						  ISelector::status_t status)
{
	typedef typename GridObjectCollection::traits<TElem>::iterator	TIter;
	GridObjectCollection goc = sh.get_grid_objects_in_subset(subsetIndex);

	for(size_t lvl = 0; lvl < goc.num_levels(); ++lvl){
		for(TIter iter = goc.begin<TElem>(lvl); iter != goc.end<TElem>(lvl); ++iter)
			sel.select(*iter, status);
	}
}
number FaceArea(ISubsetHandler& sh, int si, size_t lvl, TAAPosVRT& aaPos)
{
	number sum = 0.;
	GridObjectCollection goc = sh.get_grid_objects_in_subset(si);

	if (goc.num<Face>(lvl) == 0) {
		UG_WARNING("WARNING: Given subset doesn't contain any faces on given level.");
	} else {
		typedef geometry_traits<Face>::const_iterator CIT;
		for (CIT cit = goc.faces_begin(lvl); cit != goc.faces_end(lvl); cit++)
			sum += FaceArea(*cit, aaPos);
	}

	return sum;
}
void FindSubsetGroups
(
	std::vector<int> & minCondInd,
	const std::vector<bool> & isMarked,
	const ISubsetHandler & sh,
	const NeighborhoodType nbhType
)
{
	typedef typename geometry_traits<TBaseObj>::const_iterator elem_iterator;
	
	UG_ASSERT (((int) isMarked.size ()) == sh.num_subsets (), "FindSubsetGroups: array size mismatch");
	
	std::vector<TBaseObj*> neighbours;
	
//	Prepare minCondInd
	minCondInd.resize (sh.num_subsets ());
	for (size_t si = 0; si < minCondInd.size (); si++)
		minCondInd [si] = (isMarked [si])? si : -1;
	
//	Loop over the subsets:
	for (size_t si = 0; si < minCondInd.size (); si++)
	{
		int min_si;
		
	//	Marked subset?
		if ((min_si = minCondInd [si]) < 0)
			continue; // no, we do not treat this subset
		
	//	Yes, loop over the elements in the subdomain (in the grid level 0):
		GridObjectCollection goc = sh.get_grid_objects_in_subset (si);
		elem_iterator e_end = goc.end<TBaseObj> (0);
		bool is_empty = true;
		for (elem_iterator e_iter = goc.begin<TBaseObj> (0); e_iter != e_end; ++e_iter)
		{
			is_empty = false;
		//	Loop over the neighbours:
			CollectNeighbors (neighbours, *e_iter, *sh.grid(), nbhType);
			for (size_t k = 0; k < neighbours.size (); k++)
			{
				int min_nbr_si;
				int nbr_si = sh.get_subset_index (neighbours [k]);
				
				if (nbr_si < 0 || nbr_si >= (int) minCondInd.size ())
					UG_THROW ("FindSubsetGroups: Illegal neighbour subset index.");
				if ((min_nbr_si = minCondInd [nbr_si]) < 0)
					continue; // we do not treat this subset
				
			//	Set the same smallest index to both groups of the subsets:
				if (min_nbr_si < min_si)
				{
					for (size_t l = 0; l < minCondInd.size (); l++)
						if (minCondInd [l] == min_si)
							minCondInd [l] = min_nbr_si;
				}
				else if (min_nbr_si > min_si)
				{
					for (size_t l = 0; l < minCondInd.size (); l++)
						if (minCondInd [l] == min_nbr_si)
							minCondInd [l] = min_si;
				}
			}
		}
		if (is_empty) minCondInd [si] = -2;
	}
}