[Dune] GridFactory with UG collapses at 100000 nodes

[Dominic Kempf]

Hey Dune-Team!

I am using the Dune::GridFactory with UG to create large cube grids. But 
there seems to be a bug, that makes grid generation extremly slow at 
exactly 100000 inserted nodes. I ran a loop that creates cube grids on 
the unit square with increasing number of nodes. The result was that 
until 99000 the grid was instantly created, as soon as I passed the 
100000, it takes around 10 seconds. Much larger grids are impossible to 
create due to computing time. This doesnt seem to be a memory issue, 
increasing UG's default heap size doesnt change a thing. I can still get 
bigger grids by refinement in acceptable time, but this brings some 
other issues with it for me.

This is the example code I extracted, that makes the issue obvious:

   typedef Dune::UGGrid<2> Grid;

   for (double n=95000; n<103000; n += 1000)
   {
     int m = (int)sqrt(n);
     Dune::GridFactory<Grid> factory;
     for (int j = 0; j < m+1; j++)
       for (int i = 0; i < m+1; i++)
       {
         //set vertex position
         Dune::FieldVector<Grid::ctype,2> pos;
         pos[0] = ((double)i)/m;
         pos[1] = ((double)j)/m;
         factory.insertVertex(pos);
       }

     //get geometry type
     const Dune::GeometryType gt(Dune::GeometryType::cube,2);

     //insert elements
     for (unsigned int i=0; i<m;i++)
       for (unsigned int j=0; j<m;j++)
       {
         //set node positions
         std::vector<unsigned int> pos;
         pos.push_back(i+j*(m+1));
         pos.push_back(i+1+j*(m+1));
         pos.push_back(i+(j+1)*(m+1));
         pos.push_back(i+1+(j+1)*(m+1));
         factory.insertElement(gt,pos);
       }
     Grid* grid = factory.createGrid();
     std::cout << "Grid with " << grid->size(2) << " vertices created!\n";
     delete grid;
   }


  I hope somebody could help!
Thanks in advance!
Dominic