Skip to content

Added support for ParMETIS with `real_t != float`

Simon Praetorius requested to merge simon.praetorius/dune-istl:issue/parmetis_real_t into master

This MR fixes #45 (closed)

Starting with version ParMETIS 4.0 the typedef real_t is introduced to allow different floating-point types for e.g. weights depending on the macro REALTYPEWIDTH. Also, the typedef idx_t is introduced to specify the integer type of indices, depending on the macro IDXTYPEWIDTH. Now, the corresponding typedefs are used instead of fixing the types to float and int.

When (PT)Scotch(Par)METIS is used, the index type is given by SCOTCH_Num, while the floating-point type is fixed to float.

Synopsis

  • Added namespace Dune::Metis
  • Added typedefs real_t and idx_t in namespace Metis, depending on configuration (with parmetis, with scotchmetis, or without). These names follow the original names introduced in the Metis library.
  • Changed all occurences of idxtype to Metis::idx_t and float in the signature of parmetis calls to Metis::real_t

Discussion

Some users prefer the Scotch library over ParMETIS due to license restrictions. But, unfortunately, up to now the metis.h and parmetis.h provided by Scotch are not self-containing, i.e. the defined interfaces rely on a type SCOTCH_Num that is not defined in metis.h. Thus, Scotch need to be patched in order to to be usable in the same way as Metis and ParMetis.

Problem: There is no common way to patch the library. Everyone makes it differently. In Debian 9, there is no SCOTCH_Num introduced, but simply the interface rewritten with explicit types. In Debian 10, the file scotch.h is included inside metis.h. In the patch provided by @markus.blatt a typedef was introduced in metis.h and parmetis.h. One can not detect, by looking in the header file, what kind of patch is implemented.

Proposed solution: By default, Scotch uses int as SCOTCH_Num type. So, I stick on this. Only if the user sets -DHAVE_SCOTCH_NUM_TYPE I use SCOTCH_Num. So, it compiles as before, but gives additional flexibility. Maybe one can add a cmake compile-test to find out whether SCOTCH_Num is provided or not.

TODO

  • Test with libscotchmetis from debian9 and self-compiled scotch using patch from @markus.blatt
  • Cleanup of commit history
Edited by Simon Praetorius

Merge request reports