PhiJAX is a typed JAX framework for physics-informed neural networks (PINNs). It provides the core tools for training PINNs: functional state, explicit-key sampling, reusable equations and objectives, adaptive loss balancing, callbacks, logging, checkpointing, and prediction artifacts. Its Trainer and PhiModule lifecycles are inspired by Lightning.

For a configuration-first project layout, start from phijax-hydra-template and customize its entrypoints, Hydra configs, and application DataModules.

Beta API: PhiJAX is under active development. Breaking changes may occur between major versions and during the beta period before the stable release. The supported public API is documented in package __all__ declarations. Checkpoints can be restored by compatible PhiJAX releases from the same major and minor version.

Quickstart | Guides | API reference | Changelog | Contributing

Why PhiJAX?

JAX provides automatic differentiation, vectorization, compilation, and accelerator support. PhiJAX adds the structure needed to build reproducible, maintainable PINN experiments:

• selective coordinate derivatives and reusable PDE, boundary, and data-fidelity equations;
• named objective terms with static, gradient-norm, and exact-NTK loss balancing;
• standard MLP, Modified MLP, and adaptive-residual PirateNet architectures with a custom NNX adapter;
• explicit model, optimizer, balancer, and PRNG state for reproducible compiled updates;
• familiar, Lightning-inspired lifecycles for trainers, modules, DataModules, callbacks, loggers, and checkpoints; and
• scientific data preparation on the CPU, automatic batch placement by the Trainer, and prediction files with a stable, versioned format.

PhiJAX reduces boilerplate for training, prediction, logging, and checkpointing without hiding JAX transformations or functional state. Hydra support is optional, and the core Trainer API does not depend on a configuration framework.

Installation

PhiJAX requires Python 3.12 or newer. Python 3.12, 3.13, and 3.14 are covered by CI.

pip install phijax

The default installation includes CPU-capable JAX. Select one mutually exclusive GPU extra when the matching NVIDIA runtime is available:

pip install "phijax[cuda12]"
# or
pip install "phijax[cuda13]"

Optional experiment loggers are installed separately:

pip install "phijax[tensorboard]"
pip install "phijax[wandb]"

Extras can be combined when an environment needs GPU support and both logging integrations:

pip install "phijax[cuda13,wandb,tensorboard]"

Replace cuda13 with cuda12 for a CUDA 12 environment; do not install both CUDA extras together.

Experimental TPU environments can use pip install "phijax[tpu]". The TPU, CUDA 12, and CUDA 13 extras are mutually exclusive.

See the installation guide for environment verification and development setup.

Quickstart

The first runnable example solves a one-dimensional heat equation with initial, boundary, and PDE losses. It uses no external data and runs on CPU after JAX completes its initial compilation:

git clone https://github.com/HangJung97/PhiJAX.git
cd PhiJAX
uv sync
JAX_PLATFORMS=cpu uv run --no-sync python examples/quickstart.py

JAX_PLATFORMS=cpu keeps the whole process strictly CPU-only. This is stronger than selecting Trainer(accelerator="cpu"), which controls PhiJAX placement without changing JAX's process-wide default backend.

To run the same example on an available NVIDIA GPU:

uv sync --extra cuda13
XLA_PYTHON_CLIENT_PREALLOCATE=false \
  uv run --no-sync python examples/quickstart.py --accelerator gpu

Replace cuda13 with cuda12 when using the CUDA 12 extra. Disabling preallocation prevents JAX from reserving most GPU memory at startup, which is helpful on shared or memory-constrained systems.

Read the annotated quickstart for the equation, complete source, and an explanation of each runtime object.

Core workflow

PhiJAX keeps each part of a PINN workflow explicit while assembling the common training path for you:

Model factory + objective ---> PhiModule blueprint ----+
DataModule -------------------> named batches ---------+---> Trainer.fit() ---> FitResult ---> Trainer.predict()
Optimizer + seed --------------------------------------+
LossBalancer + update policy (optional) ---------------+

The Trainer initializes the model, splits independent PRNG streams, prepares data sources, compiles the update, moves batches to devices, runs hooks, restores checkpoints, and cleans up resources. FitResult returns the bound module and explicit TrainState for prediction or advanced workflows.

Application DataModules implement setup(), train_batch_source(), and optionally predict_batch_source(). Prediction is skipped cleanly when a DataModule has no prediction source.

Trainer manages setup and cleanup automatically across fitting and prediction.

Core APIs

• Trainer.fit() assembles the common application workflow; fit_state() exposes explicit state and plan control.
• Trainer.predict() consumes a FitResult; predict_state() supports checkpoint templates and custom state.
• TrainingPlan and TrainState remain public advanced contracts for custom compiled execution.
• BasePhiModule and PhiModule provide overridable fit and prediction hooks without owning optimizers or balancers.
• PhiDataModule owns host data and explicit-key batch sources. The Trainer owns device placement.
• ModelFactory and InitializedModel let any JAX architecture expose a pure apply callable, state, and summary.
• LossBalancer supports arbitrary JAX-compatible state and exposes diagnostics without a prescribed state layout.
• Derivative, equation, objective, callback, logger, evaluation, and artifact APIs can be reused across projects.
• Hydra instantiation helpers and OmegaConf resolvers are available under phijax.integrations without coupling the Trainer to Hydra.

Only names documented in package __all__ declarations are supported public imports.

Checkpoints and prediction artifacts

PhiJAX saves complete training state in versioned checkpoints and produces portable prediction artifacts for downstream evaluation. Restoration raises an error when a checkpoint version is incompatible.

Development

Install all development dependencies, then enable the repository hooks:

uv sync --group all
uv run --no-sync pre-commit install

Run the local validation suite before submitting a change:

JAX_PLATFORMS=cpu uv run --no-sync pytest
uv run --no-sync ruff check .
uv run --no-sync ruff format --check .
uv run --no-sync pyright
uv run --no-sync mkdocs build --strict
uv run --no-sync pre-commit run --all-files

See the documentation for the complete API and extension guides.

Contributing

Contributions are welcome. Read the contribution guide for the development workflow, testing expectations, documentation requirements, and pull-request checklist.

License

PhiJAX is distributed under the Apache License 2.0.