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Fix elasticity stress #311

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Merged
inducer merged 4 commits into from
Oct 9, 2026
Merged

Fix elasticity stress #311

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834da3e
fix: coefficient in elasticity stress
alexfikl Oct 9, 2026
2570049
fix: sign difference in elasticity stress
alexfikl Oct 9, 2026
eb7bf3a
test: check stress kernels against definitions
alexfikl Oct 9, 2026
c6eadf1
chore: update baseline
alexfikl Oct 9, 2026
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176 changes: 176 additions & 0 deletions .basedpyright/baseline.json
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17531,6 +17531,182 @@
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Expand Down
6 changes: 3 additions & 3 deletions sumpy/kernel.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1116,9 +1116,9 @@ def __init__(self,
d[icomp] / r**2 * delta_jk
+ d[jcomp] / r**2 * delta_ik
- d[kcomp] / r**2 * delta_ij)
+ 3 * d[icomp] * d[jcomp] * d[kcomp] / r**4
+ 2 * d[icomp] * d[jcomp] * d[kcomp] / r**4
)
scaling = -1/(4*var("pi")*(1 - nu))
scaling = 1/(4*var("pi")*(1 - nu))
elif dim == 3:
expr = (
(1 - 2*nu) * (
Expand All @@ -1127,7 +1127,7 @@ def __init__(self,
- d[kcomp] / r**3 * delta_ij)
+ 3 * d[icomp] * d[jcomp] * d[kcomp] / r**5
)
scaling = -1/(8*var("pi")*(1 - nu))
scaling = 1/(8*var("pi")*(1 - nu))
else:
raise NotImplementedError(f"unsupported dimension: '{dim}'")

Expand Down
4 changes: 2 additions & 2 deletions sumpy/test/test_kernels.py
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Original file line number Diff line number Diff line change
Expand Up @@ -168,7 +168,7 @@ def test_p2e_multiple(
extra_kwargs["k"] = 0.2 * (0.707 + 0.707j)
else:
extra_kwargs["k"] = 0.2
if isinstance(base_knl, StokesletComponentKernel):
elif isinstance(base_knl, StokesletComponentKernel):
extra_kwargs["mu"] = 0.2

source_kernels = [
Expand Down Expand Up @@ -313,7 +313,7 @@ def test_p2e2p(
extra_kwargs["k"] = 0.2 * (0.707 + 0.707j)
else:
extra_kwargs["k"] = 0.2
if isinstance(base_knl, StokesletComponentKernel):
elif isinstance(base_knl, StokesletComponentKernel):
extra_kwargs["mu"] = 0.2

if with_source_derivative:
Expand Down
95 changes: 95 additions & 0 deletions sumpy/test/test_misc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -205,6 +205,101 @@ def test_pde_check_kernels(actx_factory: ArrayContextFactory, knl_info, order=5)
# }}}


# {{{ test_stress_kernel_definition


@pytest.mark.parametrize("dim", [2, 3])
@pytest.mark.parametrize(["name", "kernel_kwargs"], [
("stokes", {"mu": 2.5}),
("elasticity", {"mu": 2.5, "nu": 0.2}),
("brinkman", {"mu": 2.5, "k": 1.3}),
])
def test_stress_kernel_definition(
dim: int, name: str, kernel_kwargs: dict[str, float]
) -> None:
from itertools import product

rng = np.random.default_rng(42)
dvec = sym.make_sym_vector("d", dim)
kernel_kwargs = {
sym.SpatialConstant(k).as_sympy().name: v for k, v in kernel_kwargs.items()
}

def evalf(expr: sym.Expr) -> complex:
if sym.USE_SYMENGINE:
return complex(expr.n(prec=100))
else:
return complex(expr.evalf(30))

def pressure_expr(i: int) -> sym.Expr:
kernel = LaplaceKernel(dim)
expr = kernel.get_global_scaling_const() * kernel.get_expression(dvec)
return expr.diff(dvec[i])

def stokeslet_expr(i: int, j: int) -> sym.Expr:
u = StokesletComponentKernel(dim, i, j)
return u.get_global_scaling_const() * u.get_expression(dvec)

def brinkmanlet_expr(i: int, j: int) -> sym.Expr:
u = BrinkmanletComponentKernel(dim, i, j)
return u.get_global_scaling_const() * u.get_expression(dvec)

def elasticity_expr(i: int, j: int) -> sym.Expr:
u = ElasticityComponentKernel(dim, i, j)
return u.get_global_scaling_const() * u.get_expression(dvec)

def ref_stokes_stress(i: int, j: int, k: int) -> sym.Expr:
mu = sym.SpatialConstant("mu").as_sympy()
return (
-pressure_expr(j) * int(i == k)
+ mu * (stokeslet_expr(i, j).diff(dvec[k])
+ stokeslet_expr(k, j).diff(dvec[i]))
)

def ref_brinkman_stress(i: int, j: int, k: int) -> sym.Expr:
mu = sym.SpatialConstant("mu").as_sympy()
return (
-pressure_expr(j) * int(i == k)
+ mu * (brinkmanlet_expr(i, j).diff(dvec[k])
+ brinkmanlet_expr(k, j).diff(dvec[i]))
)

def ref_elasticity_stress(i: int, j: int, k: int) -> sym.Expr:
mu = sym.SpatialConstant("mu").as_sympy()
nu = sym.SpatialConstant("nu").as_sympy()
lm = 2 * mu * nu / (1 - 2 * nu)

return (
lm * int(i == j) * sum(
elasticity_expr(d, k).diff(dvec[d]) for d in range(dim)
) + mu * (elasticity_expr(i, k).diff(dvec[j])
+ elasticity_expr(j, k).diff(dvec[i]))
)

for ijk in product(range(dim), repeat=3):
if name == "stokes":
kernel = StressletComponentKernel(dim, *ijk)
stress = kernel.get_global_scaling_const() * kernel.get_expression(dvec)
ref = ref_stokes_stress(*ijk)
elif name == "elasticity":
kernel = ElasticityStressComponentKernel(dim, *ijk)
stress = kernel.get_global_scaling_const() * kernel.get_expression(dvec)
ref = ref_elasticity_stress(*ijk)
elif name == "brinkman":
kernel = BrinkmanStressComponentKernel(dim, *ijk)
stress = kernel.get_global_scaling_const() * kernel.get_expression(dvec)
ref = ref_brinkman_stress(*ijk)
else:
raise AssertionError

for _ in range(3):
point = dict(zip(dvec, rng.uniform(0.3, 1.2, dim), strict=True))
ratio = evalf((stress / ref).subs({**kernel_kwargs, **point}))
assert abs(ratio - 1) < 1.0e-10, f"{kernel}: got ratio {ratio}"

# }}}


# {{{ test_pde_check

@pytest.mark.parametrize("dim", [1, 2, 3])
Expand Down
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