zoomy_amrex._constants

Emit zoomy_core’s march constants into a C++ header (mandate 6a).

The user law: no numerical constant is hard-coded in a backend. amrex’s ComputeDt computed dt = cfl * dx / lambda, i.e. it had re-derived core’s CFL law and lost two factors of it: the mesh-dimension divisor d and the reconstruction-degree divisor (2k+1). Core’s law is

dt = c_cfl * 2 * r_in / (c_cfl_dimension * c_cfl_degree_factor * lambda)

and for a Cartesian FV cell r_in = dx/2, so it collapses to c_cfl * dx / (d * (2k+1) * lambda). Measured consequence of the omission: 1-D order 1 was correct by coincidence (d = 1, 2k+1 = 1), while 2-D order 2 was taking steps 6x larger than the law allows.

The fix is NOT to write / (2.0 * 3.0) in the driver — that would satisfy 6a’s letter while re-creating exactly the drift it exists to stop. The values come from core.

SCOPE, stated plainly: only the three CFL constants are consumed today. march_constants also resolves c_kp_eps / c_eps_h / c_dt_max / c_mood_h_bound, and those sites in this backend are still literal — a REPORTED remainder of 6a here (cid=79 has the full inventory), not a claim that 6a is finished for amrex.

Mirrors zoomy_foam/_constants.py deliberately: same shape, same failure modes, so the two backends stay comparable under the blueprint audit.

Module Contents

Functions

march_constants_for	Resolve core’s march constants for nsm.
render	Render the consumed constants as a ZoomyConstants namespace.
write_march_constants	Emit MarchConstants.H next to the other generated headers.

Data

CONSUMED

API

zoomy_amrex._constants.CONSUMED

(‘c_cfl’, ‘c_cfl_dimension’, ‘c_cfl_degree_factor’)

zoomy_amrex._constants.march_constants_for(nsm, *, cfl: float = 0.9, dimension: int = 1, degree: int = 0)

Resolve core’s march constants for nsm.

Thin, deliberate wrapper: the resolution logic lives in core and is never re-implemented here. cfl is the user’s pure SAFETY FACTOR (law: 0.9) — NOT an effective Courant number. The dimensional reduction is c_cfl_dimension’s job, so passing 0.45 for a 2-D case would apply the factor twice and halve every step.

zoomy_amrex._constants.render(consts) → str

Render the consumed constants as a ZoomyConstants namespace.

zoomy_amrex._constants.write_march_constants(nsm, out: pathlib.Path, **kw) → pathlib.Path

Emit MarchConstants.H next to the other generated headers.