Clarify install docs

[connorjward]

• Add minimal set of packages to docs so it is clear that PETSc will download most of the external packages.
• Add link to HPC installation wiki page.

Thanks to Golo Wimmer for the suggestions.

[JHopeCollins]

Are MPI and BLAS really essential system packages? I thought we were trying to avoid enforcing particular MPI implementations. Sure it's generally better to use the system one but a different one should work fine.

[connorjward]

Are MPI and BLAS really essential system packages? I thought we were trying to avoid enforcing particular MPI implementations. Sure it's generally better to use the system one but a different one should work fine.

Yeah I guess that that is a bit confusing. I guess I have conflated "tools needed to compile PETSc" with "tools that even PETSc cannot provide". Those sets don't quite fully overlap because of things like --download-mpich and --download-openblas. Please see my suggested change: https://github.com/firedrakeproject/firedrake/pull/4366/files#r2166511543

[JHopeCollins]

Are MPI and BLAS really essential system packages? I thought we were trying to avoid enforcing particular MPI implementations. Sure it's generally better to use the system one but a different one should work fine.

Yeah I guess that that is a bit confusing. I guess I have conflated "tools needed to compile PETSc" with "tools that even PETSc cannot provide". Those sets don't quite fully overlap because of things like --download-mpich and --download-openblas. Please see my suggested change: #4366 (files)

Thanks, I think the documentation is clearer now.

However, MPI and BLAS are still included in the BASE_*_PACKAGES lists in firedrake-configure.
If we're saying we will provide a minimal list of packages that the user needs to provide because PETSc just can't provide them at all, then it really should be that minimal set. At the moment there's the caveat that some unspecified subset of the --minimal-system-packages (that includes at least MPI and BLAS) can actually be provided by PETSc.

The signposting in the docs would then be the other way around - pointing out that MPI and BLAS will in fact be system packages in the vast majority of cases but not by necessity.

[connorjward]

Are MPI and BLAS really essential system packages? I thought we were trying to avoid enforcing particular MPI implementations. Sure it's generally better to use the system one but a different one should work fine.

Yeah I guess that that is a bit confusing. I guess I have conflated "tools needed to compile PETSc" with "tools that even PETSc cannot provide". Those sets don't quite fully overlap because of things like --download-mpich and --download-openblas. Please see my suggested change: #4366 (files)

Thanks, I think the documentation is clearer now.

However, MPI and BLAS are still included in the BASE_*_PACKAGES lists in firedrake-configure. If we're saying we will provide a minimal list of packages that the user needs to provide because PETSc just can't provide them at all, then it really should be that minimal set. At the moment there's the caveat that some unspecified subset of the --minimal-system-packages (that includes at least MPI and BLAS) can actually be provided by PETSc.

The signposting in the docs would then be the other way around - pointing out that MPI and BLAS will in fact be system packages in the vast majority of cases but not by necessity.

Thanks. Addressed.

[JHopeCollins]

Thanks for updating that. I have one small suggestion to make it clear that we're happy for anyone to contribute to the HPC docs, but I'm happy with this.