Flux.py

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# This file is part of the ExaHyPE2 project. For conditions of distribution and
# use, please see the copyright notice at www.peano-framework.org
from __future__ import annotations
 
from .PDETerm import PDETerm
 
 
class Flux(PDETerm):
    """!
 
    The conservative flux F(Q) of a hyperbolic PDE
 
    See python/exahype2/solvers/fv/riemann/kernels.py for the legacy
    equivalent, which additionally threads h/t/dt through the signature.
    This new API's flux() is, for now, deliberately reduced to
 
    @code
    virtual void flux(
      const double* __restrict__                   Q, // Q[{{NUMBER_OF_UNKNOWNS}}+{{NUMBER_OF_AUXILIARY_VARIABLES}}]
      const tarch::la::Vector<Dimensions, double>& x,
      int                                          normal,
      double* __restrict__                         F // F[{{NUMBER_OF_UNKNOWNS}}]
    );
    @endcode
 
    h/t/dt will return once PDE terms are tied to real C code snippets with
    proper signatures; until then every term merely gets position, normal
    (where physically meaningful) and its input/output.
 
    Q holds unknowns+auxiliary_variables entries, whereas the output F only
    holds unknowns entries: only the actual unknowns are subject to the
    hyperbolic formulation, auxiliary variables are not.
 
    """
 
    SIGNATURE = (
        "const double* __restrict__ Q, "
        "const tarch::la::Vector<Dimensions, double>& x, "
        "int normal, "
        "double* __restrict__ F"
    )
 
    NAME = "flux"
 
    def __init__(
        self,
        implementation: str = None,
        stateless: bool = False,
    ):
        """!
 
        implementation: str
          A C++ snippet that becomes flux()'s body (the empty string is a
          valid, generated no-op body), or None (the default) to leave
          flux() pure virtual for you to implement by hand. Don't add this
          term to a solver at all if the PDE has no flux contribution.
 
        """
        super().__init__(
            name=self.NAMENAME,
            implementation=implementation,
            stateless=stateless,
        )
 
    class Generator(PDETerm.Generator):
        """!
 
        Flux-specific code generation
 
        Reuses PDETerm.Generator's declaration/definition/GPU-offload logic
        as-is - Flux.SIGNATURE is picked up automatically. Declared
        explicitly (rather than left to be inherited implicitly) so that
        Flux.Generator is the obvious place to add flux-specific generation
        behaviour later, and so flux_term.generator reports its type as
        Flux.Generator rather than the more generic PDETerm.Generator.
 
        """