`migrate` — Convert a Monolithic Model¶

The migrate command takes a traditional single-file MCNP input deck and decomposes it into a Gitronics project structure.

Synopsis¶

gitronics migrate <MCNP_INPUT> [--output-path <DIR>]

Argument	Description
`MCNP_INPUT`	Path to the original monolithic MCNP input file.
`-o`, `--output-path`	Root directory for the new project. Defaults to `./project`.

Example¶

gitronics migrate models/tokamak_2025.mcnp --output-path ./tokamak_project

What it produces¶

<output-path>/
├── configurations/
│   └── baseline.yaml             ← reproduces the original model exactly
├── output/
│   └── .gitignore                ← ignores all build outputs in git
└── reference_model/
    ├── envelope_structure.mcnp   ← level-0 cells
    ├── envelope_structure.metadata
    └── filler_models/
        ├── universe_<id>.mcnp    ← one file per universe
        ├── universe_<id>.metadata
        └── ...

How universes are extracted¶

Each universe found in the model is written to its own universe_<id>.mcnp file. Cells belonging to universe 0 (the root lattice) are retained in the envelope structure.

Metadata files¶

Each filler model is accompanied by a .metadata YAML file. These files describe how the filler should be placed and can specify per-envelope transformation cards. Edit them to add transformations after migration.

Verifying the round-trip¶

After migration, rebuild the model and verify it matches the original:

gitronics build tokamak_project/configurations/baseline.yaml \
    --output-path tokamak_project/output
diff models/tokamak_2025.mcnp tokamak_project/output/assembled.mcnp

Note

Minor formatting differences (whitespace, line ordering within a section) are expected. The geometry and physics data should be functionally identical.

Limitations¶

Data cards (materials, tallies, source) are written to a single data_cards.source file. After migration you may wish to split these into separate files under reference_model/data_cards/.
The migration does not attempt to detect repeated structures or simplify the model.

migrate — Convert a Monolithic Model¶