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Bug#842135: release.debian.org: nmu: slepc4py_3.7.0-2+b3

On Wed, 26 Oct 2016 10:37:40 +0200 Emilio Pozuelo Monfort <pochu@debian
.org> wrote:
> Done, including deal.ii getdp slepc4py and dolfin.

> I don't quite understand why slepc and petsc have versioned packages
and use
> alternatives to provide the shared library, but I haven't looked
closely at it.
> Not sure I want to though :P

Since you asked ;) ...

PETSc upstream has arranged the library so that the preferred version
can be easily identified with env variable PETSC_DIR.

Each installation (referenced by PETSC_DIR) is patch specific, i.e. the
library is located in /usr/lib/petscdir/3.7.3 or
/usr/lib/petscdir/3.7.4 etc. This allows the "flexibility" of parallel
installation of different patch versions.

But the soname only contains the minor version, 3.7 not 3.7.4.

slepc just follows the structure of petsc.

I guess what you're asking is why upstream bothers providing patch-
specific installations when the soname is the same between them. 
Upstream will have to speak for themselves, but I could imagine that
doing it that way makes it easier to manage installations on high
performance supercomputers.  Installations on the supercomputers tend
to be conservative. They worry about differences in the results of
computations arising from different patch versions, even though the
client software will happily run with any version with the same soname.

Whatever upstream's reasons might be,  I've set up the Debian packaging
to reflect this patch-version "flexibility" provided by the upstream
directory structure.


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