Commit db66c16b authored by Martin Bauer's avatar Martin Bauer
Browse files

Added forth order FD stencil for 2D, first derivatives

parent 6dd3ba55
from typing import Tuple
import sympy as sp
from functools import partial
from pystencils.cache import memorycache
from pystencils import AssignmentCollection, Field
from pystencils.fd import Diff
from .derivative import diff_args
from .derivation import FiniteDifferenceStencilDerivation
def fd_stencils_standard(indices, dx, fa):
......@@ -51,6 +54,19 @@ def fd_stencils_isotropic(indices, dx, fa):
raise NotImplementedError("Supports only derivatives up to order 2 for 1D and 2D setups")
def fd_stencils_forth_order_isotropic(indices, dx, fa):
order = len(indices)
if order != 1:
raise NotImplementedError("Forth order finite difference discretization is "
"currently only supported for first derivatives")
dim = indices[0]
if dim not in (0, 1):
raise NotImplementedError("Forth order finite difference discretization is only implemented for 2D")
stencils = forth_order_2d_derivation()
return stencils[dim].apply(fa) / dx
def fd_stencils_isotropic_high_density_code(indices, dx, fa):
dim = fa.field.spatial_dimensions
if dim == 1:
......@@ -106,3 +122,29 @@ def discretize_spatial(expr, dx, stencil=fd_stencils_standard):
new_args = [discretize_spatial(a, dx, stencil) for a in expr.args]
return expr.func(*new_args) if new_args else expr
# -------------------------------------- special stencils --------------------------------------------------------------
def forth_order_2d_derivation() -> Tuple[FiniteDifferenceStencilDerivation.Result, ...]:
# Symmetry, isotropy and 4th order conditions are not enough to fully specify the stencil
# one weight has to be specifically set to a somewhat arbitrary value
second_neighbor_weight = sp.Rational(1, 10)
second_neighbor_stencil = [(i, j)
for i in (-2, -1, 0, 1, 2)
for j in (-2, -1, 0, 1, 2)
x_diff = FiniteDifferenceStencilDerivation((0,), second_neighbor_stencil)
x_diff.set_weight((2, 0), second_neighbor_weight)
x_diff.assume_symmetric(0, anti_symmetric=True)
x_diff_stencil = x_diff.get_stencil(isotropic=True)
y_diff = FiniteDifferenceStencilDerivation((1,), second_neighbor_stencil)
y_diff.set_weight((0, 2), second_neighbor_weight)
y_diff.assume_symmetric(1, anti_symmetric=True)
y_diff_stencil = y_diff.get_stencil(isotropic=True)
return x_diff_stencil, y_diff_stencil
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