Read and write different stella input versions

Read and write different stella input versions#

Stella’s Fortran namelist input format was restructured in v1.0: what were ~10 large namelists in earlier releases became ~30+ smaller, purpose-specific namelists. Pyrokinetics supports three format families:

Version

Marker namelists

LEGACY

knobs, parameters, physics_flags

PRE_V1

parameters_physics, parameters_numerical

V1

geometry_options, gyrokinetic_terms, kxky_grid_* …

Reading#

Pyrokinetics auto-detects the format on read — no user action required:

from pyrokinetics.gk_code import GKInputSTELLA

gk = GKInputSTELLA("my_input.in")
print(gk._format_version.value)   # "legacy", "pre_v1", or "v1"

All three formats expose the same physics through get_local_geometry(), get_local_species(), and get_numerics().

Writing#

The format of a written file is determined by the template that was used to initialise the Pyro object for stella. Two templates ship with pyrokinetics:

Write v1 (default)#

from pyrokinetics import Pyro, template_dir

pyro = Pyro(gk_file=template_dir / "input.cgyro", gk_code="CGYRO")
pyro.write_gk_file(file_name="out.in", gk_code="STELLA")   # -> v1

Write pre-v1#

Pass the pre-v1 template explicitly when creating the stella context:

pyro.write_gk_file(
    file_name="out.in",
    gk_code="STELLA",
    template_file=template_dir / "input.stella_pre_v1",
)

Note

template_file is honoured only when the stella context is created by this call (i.e. gk_code="STELLA" is passed alongside). If a stella context already exists on the Pyro object, the existing template dictates the output format.

Upgrading legacy files to v1#

Pyrokinetics reads legacy files directly. If you need to emit a legacy input as v1 on disk, read it with pyrokinetics and write it back — the output defaults to v1:

pyro = Pyro(gk_file="old_stella.in", gk_code="STELLA")
pyro.write_gk_file(file_name="upgraded_v1.in")

Alternatively, stella ships an authoritative converter at $STELLA/AUTOMATIC_TESTS/convert_input_files/convert_inputFile.py that upgrades namelists directly without going through pyrokinetics.

Full worked example#

See docs/examples/example_cgyro_to_stella.py — it reads a CGYRO input and writes both v1 and pre-v1 stella files, verifying the physics is preserved.

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