Parallel tipsy

[The9Cat]

The issue

Current implementation of tipsy file reading does not allow for per-process partitioning. This requires each process to read the entire file.

Fix

• Added partitioning based on MPI process rank for both XDR and native versions
• Use std::runtime_error class for exception handling
• Added a pyEXP utility for intialized C++ side MPI communicators and variables. Not necessary for MPI coefficient generation but will be helpful for other C++ MPI aware classes

Notes

• Tested with mpi4py on one of Jason's large Bonsai-generated simulation snapshots

[Copilot]

Pull Request Overview

This PR adds MPI-aware parallel partitioning support for tipsy file reading to enable per-process data distribution instead of requiring each process to read the entire file.

• Added MPI-based partitioning logic for both XDR and native tipsy file readers
• Implemented robust exception handling using std::runtime_error
• Added utility function for initializing C++ MPI communicators from pyEXP

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pyEXP/UtilWrappers.cc	Adds setMPI function to initialize C++ MPI communicators and variables
include/tipsy.H	Updates tipsy header structures and adds parallel reading support with index offset tracking
include/SLGridMP2.H	Adds static variables for radial boundary heuristics in grid construction
include/ParticleReader.H	Updates constructors and adds new Bonsai type for ID handling
exputil/SLGridMP2.cc	Implements radial boundary heuristics and improved error diagnostics
exputil/ParticleReader.cc	Updates constructors and implements new Bonsai ID handling logic
expui/Centering.cc	Fixes increment operator placement in loop condition

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[michael-petersen]

I don't have any files available to test this -- we might want to consider something like that for a test -- but everything here makes sense.