Dear Gmsh developers, I'm trying to understand the partitioned format of gmsh. I meshed a square with triangles and partitioned it with the gui of gmsh using parmetis with default settings. I have 4 partitions, bounded by 4 lines with elementary tags 1-4 (perimeter of the square) and by 5 more lines with elementary tags (-1,-2,-3,-4,-5) which separate the partitions. Looking at the '$Elements' section, I have entries (for triangles) such as:
461 2 5 0 1 2 3 -4 106 328 202 The triangle belongs to 2 partitions: 3 and 4. Unfortunately, I don't understand the explanation 'negative partition ids indicate ghost cells' from the reference manual. Which nodes of the triangle belong to partition 3/4 and which of them are 'owned' by the triangle? Does it mean that the neighbour of triangle 461 is some element in partition 4? Strangely, no triangle in the elements section lists -5 among their tags. There's only one single edge (element type 1) with elementary tag -5 in the whole mesh. When a solver reads the mesh in parallel (multiple processes read the file at the same time, each of them only its own partition), the elements whose nodes are on partition boundaries (and are possibly marked as ghost nodes) do not know directly from the mesh file which element in the neighbouring partition owns those nodes - which means that some extra searching and parallel communication is necessary to obtain this information. Is that correct? I'm not sure I understand this. Could someone please suggest an efficient way for parallel reading of a partitioned *.msh file? Can gmsh export to some other format which is more suitable for this? Thank you very much. Martin Vymazal _______________________________________________ gmsh mailing list [email protected] http://www.geuz.org/mailman/listinfo/gmsh
