nrpy 2.0.9

Python/SymPy-based code generation for numerical relativity... and beyond!

NRPy+ 2.0: Python/SymPy-Based Code Generation for Numerical Relativity... and Beyond!

Quick start:

1. pip install nrpy
2. Choose a project to build, run the provided command, then follow the instructions for compiling & running the generated C code.
   • Wave equation solver
     • Cartesian coordinates: python3 -m nrpy.examples.wave_equation_cartesian
     • Curvilinear coordinates: python3 -m nrpy.examples.wave_equation_curvilinear
   • General relativity
     • Two black holes collide: python3 -m nrpy.examples.two_blackholes_collide

Slow start, in case you want to develop NRPy+ directly:

1. Clone this repository, and cd nrpy
2. Add the repository root directory to your Python path. export PYTHONPATH=.:$PYTHONPATH . For convenience, add this command to your ~/.bashrc file: echo "export PYTHONPATH=.:\$PYTHONPATH" >> ~/.bashrc
3. Then e.g., run an example code: python3 nrpy/examples/wave_equation_cartesian, then follow the instructions for compiling & running the generated C code.
4. Run ./wavetoy. It'll output at various times the solution from the point closest to r=0, as well as the relative error compared to the exact solution at that point to a file out0d-conv_factor1.00.txt.
5. All BlackHoles@Home (BHaH) infrastructure codes now support parameter files, and each code generation automatically outputs a parfile named [project name].par. So you'll find an editable wavetoy.par.
6. In addition, users can override certain parameter file parameters at the command line. E.g., wavetoy has a parameter convergence_factor that increases the resolution (technically Nx=Ny=Nz) by this factor. To output at twice the resolution, simply run ./wavetoy 2.0, and a new file will be output out0d-conv_factor2.00.txt, which contains data at 2x the resolution.
7. Analyze the output from out0d-conv_factor1.00.txt and out0d-conv_factor2.00.txt in e.g., gnuplot.

Key Improvements over NRPy+ 1.0:

Easy Installation

• NRPy+ has been transformed into a proper Python project and can now be installed via pip! Use the command pip install nrpy to get started.
• Visit our PyPI page for more information.
  • With pip, it's easier than ever to build your own projects based on NRPy+.
  • You can now generate a complete C project from start to finish without the need for running a Jupyter notebook.
    • For instance, running pip install nrpy && python3 -m nrpy.examples.two_blackholes_collide will generate a C code project that evolves Brill-Lindquist forward in time using the BSSN formulation.
  • Check out GitHub README for instructions on generating other pre-baked example codes... or use them to generate your own codes!

Python 3.6+ Features

• NRPy+ now makes use of Python features introduced in version 3.6 and above, such as f-strings.
• The code is now more Pythonic and incorporates objects where useful. Global variables are now a thing of the past!

User-friendly

• It's much simpler to work with NRPy+ now; you no longer have to read the source code of each function you call.
  • Facilitating this, you'll find:
    • Docstrings for all functions, classes, and modules.
    • Type hints across all modules; mypy --strict passes.
    • Numerous doctests.
    • Code formatted with Black.
    • Stricter linting.

Improved Continuous Integration

• GitHub Actions now checks all files within the repo and will fail if any of the following conditions are met:
  • Doctest failure
  • pylint score less than 9.5
  • Black needs to reformat any .py file
  • mypy --strict fails on any .py file
  • Generating and compiling all examples from the pip-installed NRPy+ fresh from the latest git commit fails.

More Extensible

• The "SENR" infrastructure has been replaced with "BHaH" (BlackHoles@Home). All BHaH-specific functionality is located in nrpy/infrastructures/BHaH/.
  • While BHaH currently only supports single grids, multi-patch support will be added soon.
  • You'll notice the old paramstruct has been broken into commondata_struct (data shared by all grids) and griddata (contains data specific to a particular grid).
    • Adding multi-patch support is a matter of setting commondata.NUMGRIDS > 1 and all the special algorithms.
  • There is a common but slightly customizable main.c file used by all BHaH codes, see nrpy/infrastructures/BHaH/main_c.py. This should greatly minimize code duplication in BHaH codes.
  • Parameter files are now supported, as well as advanced command-line input.
  • The infrastructures/ directory includes helper functions for specific infrastructures. It currently contains BHaH and CarpetX subdirectories, with more to come.
  • Cparameters has been renamed to CodeParameters, allowing for future extensions of NRPy+ to output kernels in Python, Fortran, etc.
  • Rewritten expression validation infrastructure, to make it easier to validate newly added sympy expressions -- regardless of how complex they are.

Plans for Old nrpytutorial Code

• We'll migrate the Jupyter notebooks to a new nrpytutorial GitHub repo as they are updated to NRPy+ 2.0.
• All the core .py files from nrpytutorial have been modernized & ported to NRPy+ 2.0.
• What .py files remain in nrpytutorial will be ported to NRPy+ 2.0.