64-bit Mshr/Dolfin ------------- 64-bit support is provided by python3-mshr64-real and libmshr64-dev. 64-bit here refers to 64-bit indexing provided by a 64-bit build of PETSc, allowing handling of larger systems (larger meshes) with more than 2 billion degress of freedom. It is provided in Dolfin by the python3-dolfin64-real and libdolfin64-dev packages (libdolfin64.so). This is activated by setting PETSC_DIR and SLEPC_DIR to appropriate paths, e.g. PETSC_DIR=/usr/lib/petsc64 SLEPC_DIR=/usr/lib/slepc64 Depending on usage you may also need to specific the dolfin libname extension ("64") to link to libdolfin64.so rather than libdolfin.so. This is controlled via DOLFIN_LIB_NAME_EXT. Likewise, linking with libmshr64.so is facilitated via MSHR_LIB_NAME_EXT. For cmake (C++ applications), set the cmake variable cmake -DMSHR_LIB_NAME_EXT=64 -DDOLFIN_LIB_NAME_EXT=64 For python, set it as an environment variable MSHR_LIB_NAME_EXT=64 DOLFIN_LIB_NAME_EXT=64 python3 Each of PETSC_DIR (SLEPC_DIR), MSHR_LIB_NAME_EXT and DOLFIN_LIB_NAME_EXT need to be set to ensure the program links to libpetsc64_*.so, libmshr64.so and libdolfin64.so, and not their 32-bit counterparts. python3-mshr is now a base package providing a mshr.pth pointing by default at the preferred PETSc installation provided by python3-mshr-real (for PETSC_DIR=/usr/lib/petsc SLEPC_DIR=/usr/lib/slepc).