def operator(self, u):
sqrt_w = self.get_sqrt_weight()
inv_sqrt_w_u = cse(u / sqrt_w)
if self.is_unique_only_up_to_constant():
# The exterior Dirichlet operator in this representation
# has a nullspace. The mean of the density must be matched
# to the desired solution separately. As is, this operator
# returns a mean that is not well-specified.
#
# See Hackbusch, https://books.google.com/books?id=Ssnf7SZB0ZMC
# Theorem 8.2.18b
amb_dim = self.kernel.dim
ones_contribution = (sym.Ones() *
sym.mean(amb_dim, amb_dim - 1, inv_sqrt_w_u))
else:
ones_contribution = 0
return (
-self.loc_sign * 0.5 * u + sqrt_w *
(self.alpha * sym.S(self.kernel,
inv_sqrt_w_u,
qbx_forced_limit=+1,
kernel_arguments=self.kernel_arguments) -
sym.D(self.kernel,
inv_sqrt_w_u,
qbx_forced_limit="avg",
kernel_arguments=self.kernel_arguments) + ones_contribution)
)
def get_extension_bie_symbolic_operator(loc_sign=1):
"""
loc_sign:
-1 for interior Dirichlet
+1 for exterior Dirichlet
"""
logger = logging.getLogger("SETUP")
logger.info(locals())
dim = 2
cse = sym.cse
sigma_sym = sym.make_sym_vector("sigma", dim)
int_sigma = sym.Ones() * sym.integral(2, 1, sigma_sym)
nvec_sym = sym.make_sym_vector("normal", dim)
mu_sym = sym.var("mu")
stresslet_obj = StressletWrapper(dim=dim)
stokeslet_obj = StokesletWrapper(dim=dim)
bdry_op_sym = (
loc_sign * 0.5 * sigma_sym - stresslet_obj.apply(
sigma_sym, nvec_sym, mu_sym, qbx_forced_limit='avg') -
stokeslet_obj.apply(sigma_sym, mu_sym, qbx_forced_limit='avg') +
int_sigma)
return bdry_op_sym
def operator(self, u):
from sumpy.kernel import HelmholtzKernel, LaplaceKernel
sqrt_w = self.get_sqrt_weight()
inv_sqrt_w_u = cse(u / sqrt_w)
knl = self.kernel
lknl = self.laplace_kernel
knl_kwargs = {}
knl_kwargs["kernel_arguments"] = self.kernel_arguments
DpS0u = sym.Dp(
knl, # noqa
cse(sym.S(lknl, inv_sqrt_w_u)),
**knl_kwargs)
if self.use_improved_operator:
Dp0S0u = -0.25 * u + sym.Sp( # noqa
lknl, # noqa
sym.Sp(lknl, inv_sqrt_w_u, qbx_forced_limit="avg"),
qbx_forced_limit="avg")
if isinstance(self.kernel, HelmholtzKernel):
DpS0u = ( # noqa
sym.Dp(
knl - lknl, # noqa
cse(sym.S(lknl, inv_sqrt_w_u, qbx_forced_limit=+1)),
qbx_forced_limit=+1,
**knl_kwargs) + Dp0S0u)
elif isinstance(knl, LaplaceKernel):
DpS0u = Dp0S0u # noqa
else:
raise ValueError(
f"no improved operator for '{self.kernel}' known")
if self.is_unique_only_up_to_constant():
# The interior Neumann operator in this representation
# has a nullspace. The mean of the density must be matched
# to the desired solution separately. As is, this operator
# returns a mean that is not well-specified.
amb_dim = self.kernel.dim
ones_contribution = (sym.Ones() *
sym.mean(amb_dim, amb_dim - 1, inv_sqrt_w_u))
else:
ones_contribution = 0
return (
-self.loc_sign * 0.5 * u + sqrt_w *
(sym.Sp(knl, inv_sqrt_w_u, qbx_forced_limit="avg", **knl_kwargs) -
self.alpha * DpS0u + ones_contribution))
def operator(self, u, **kwargs):
"""
:param u: symbolic variable for the density.
:param kwargs: additional keyword arguments passed on to the layer
potential constructor.
"""
sqrt_w = self.get_sqrt_weight()
inv_sqrt_w_u = sym.cse(u/sqrt_w)
if self.is_unique_only_up_to_constant():
# The exterior Dirichlet operator in this representation
# has a nullspace. The mean of the density must be matched
# to the desired solution separately. As is, this operator
# returns a mean that is not well-specified.
#
# See Hackbusch, https://books.google.com/books?id=Ssnf7SZB0ZMC
# Theorem 8.2.18b
ones_contribution = (
sym.Ones() * sym.mean(self.dim, self.dim - 1, inv_sqrt_w_u))
else:
ones_contribution = 0
def S(density): # noqa
return sym.S(self.kernel, density,
kernel_arguments=self.kernel_arguments,
qbx_forced_limit=+1, **kwargs)
def D(density): # noqa
return sym.D(self.kernel, density,
kernel_arguments=self.kernel_arguments,
qbx_forced_limit="avg", **kwargs)
return (
-0.5 * self.loc_sign * u + sqrt_w * (
self.alpha * S(inv_sqrt_w_u)
- D(inv_sqrt_w_u)
+ ones_contribution
)
)
def operator(self, u, **kwargs):
"""
:param u: symbolic variable for the density.
:param kwargs: additional keyword arguments passed on to the layer
potential constructor.
"""
sqrt_w = self.get_sqrt_weight()
inv_sqrt_w_u = sym.cse(u/sqrt_w)
laplace_s_inv_sqrt_w_u = sym.cse(
sym.S(self.laplace_kernel, inv_sqrt_w_u, qbx_forced_limit=+1)
)
kwargs["kernel_arguments"] = self.kernel_arguments
# NOTE: the improved operator here is based on right-precondioning
# by a single layer and then using some Calderon identities to simplify
# the result. The integral equation we start with for Neumann is
# I + S' + alpha D' = g
# where D' is hypersingular
if self.use_improved_operator:
def Sp(density):
return sym.Sp(self.laplace_kernel,
density,
qbx_forced_limit="avg")
# NOTE: using the Calderon identity
# D' S = -u/4 + S'^2
Dp0S0u = -0.25 * u + Sp(Sp(inv_sqrt_w_u))
from sumpy.kernel import HelmholtzKernel, LaplaceKernel
if isinstance(self.kernel, HelmholtzKernel):
DpS0u = (
sym.Dp(
self.kernel - self.laplace_kernel,
laplace_s_inv_sqrt_w_u,
qbx_forced_limit=+1, **kwargs)
+ Dp0S0u)
elif isinstance(self.kernel, LaplaceKernel):
DpS0u = Dp0S0u
else:
raise ValueError(f"no improved operator for '{self.kernel}' known")
else:
DpS0u = sym.Dp(self.kernel, laplace_s_inv_sqrt_w_u, **kwargs)
if self.is_unique_only_up_to_constant():
# The interior Neumann operator in this representation
# has a nullspace. The mean of the density must be matched
# to the desired solution separately. As is, this operator
# returns a mean that is not well-specified.
ones_contribution = (
sym.Ones() * sym.mean(self.dim, self.dim - 1, inv_sqrt_w_u))
else:
ones_contribution = 0
kwargs["qbx_forced_limit"] = "avg"
return (
-0.5 * self.loc_sign * u
+ sqrt_w * (
sym.Sp(self.kernel, inv_sqrt_w_u, **kwargs)
- self.alpha * DpS0u
+ ones_contribution
)
)
def run_exterior_stokes_2d(ctx_factory,
nelements,
mesh_order=4,
target_order=4,
qbx_order=4,
fmm_order=10,
mu=1,
circle_rad=1.5,
do_plot=False):
# This program tests an exterior Stokes flow in 2D using the
# compound representation given in Hsiao & Kress,
# ``On an integral equation for the two-dimensional exterior Stokes problem,''
# Applied Numerical Mathematics 1 (1985).
logging.basicConfig(level=logging.INFO)
cl_ctx = cl.create_some_context()
queue = cl.CommandQueue(cl_ctx)
ovsmp_target_order = 4 * target_order
from meshmode.mesh.generation import ( # noqa
make_curve_mesh, starfish, ellipse, drop)
mesh = make_curve_mesh(lambda t: circle_rad * ellipse(1, t),
np.linspace(0, 1, nelements + 1), target_order)
coarse_density_discr = Discretization(
cl_ctx, mesh, InterpolatoryQuadratureSimplexGroupFactory(target_order))
from pytential.qbx import QBXLayerPotentialSource
target_association_tolerance = 0.05
qbx, _ = QBXLayerPotentialSource(
coarse_density_discr,
fine_order=ovsmp_target_order,
qbx_order=qbx_order,
fmm_order=fmm_order,
target_association_tolerance=target_association_tolerance,
_expansions_in_tree_have_extent=True,
).with_refinement()
density_discr = qbx.density_discr
normal = bind(density_discr, sym.normal(2).as_vector())(queue)
path_length = bind(density_discr, sym.integral(2, 1, 1))(queue)
# {{{ describe bvp
from pytential.symbolic.stokes import StressletWrapper, StokesletWrapper
dim = 2
cse = sym.cse
sigma_sym = sym.make_sym_vector("sigma", dim)
meanless_sigma_sym = cse(sigma_sym - sym.mean(2, 1, sigma_sym))
int_sigma = sym.Ones() * sym.integral(2, 1, sigma_sym)
nvec_sym = sym.make_sym_vector("normal", dim)
mu_sym = sym.var("mu")
# -1 for interior Dirichlet
# +1 for exterior Dirichlet
loc_sign = 1
stresslet_obj = StressletWrapper(dim=2)
stokeslet_obj = StokesletWrapper(dim=2)
bdry_op_sym = (-loc_sign * 0.5 * sigma_sym - stresslet_obj.apply(
sigma_sym, nvec_sym, mu_sym, qbx_forced_limit='avg') +
stokeslet_obj.apply(
meanless_sigma_sym, mu_sym, qbx_forced_limit='avg') -
(0.5 / np.pi) * int_sigma)
# }}}
bound_op = bind(qbx, bdry_op_sym)
# {{{ fix rhs and solve
def fund_soln(x, y, loc, strength):
#with direction (1,0) for point source
r = cl.clmath.sqrt((x - loc[0])**2 + (y - loc[1])**2)
scaling = strength / (4 * np.pi * mu)
xcomp = (-cl.clmath.log(r) + (x - loc[0])**2 / r**2) * scaling
ycomp = ((x - loc[0]) * (y - loc[1]) / r**2) * scaling
return [xcomp, ycomp]
def rotlet_soln(x, y, loc):
r = cl.clmath.sqrt((x - loc[0])**2 + (y - loc[1])**2)
xcomp = -(y - loc[1]) / r**2
ycomp = (x - loc[0]) / r**2
return [xcomp, ycomp]
def fund_and_rot_soln(x, y, loc, strength):
#with direction (1,0) for point source
r = cl.clmath.sqrt((x - loc[0])**2 + (y - loc[1])**2)
scaling = strength / (4 * np.pi * mu)
xcomp = ((-cl.clmath.log(r) + (x - loc[0])**2 / r**2) * scaling -
(y - loc[1]) * strength * 0.125 / r**2 + 3.3)
ycomp = (((x - loc[0]) * (y - loc[1]) / r**2) * scaling +
(x - loc[0]) * strength * 0.125 / r**2 + 1.5)
return [xcomp, ycomp]
nodes = density_discr.nodes().with_queue(queue)
fund_soln_loc = np.array([0.5, -0.2])
strength = 100.
bc = fund_and_rot_soln(nodes[0], nodes[1], fund_soln_loc, strength)
omega_sym = sym.make_sym_vector("omega", dim)
u_A_sym_bdry = stokeslet_obj.apply( # noqa: N806
omega_sym, mu_sym, qbx_forced_limit=1)
omega = [
cl.array.to_device(queue,
(strength / path_length) * np.ones(len(nodes[0]))),
cl.array.to_device(queue, np.zeros(len(nodes[0])))
]
bvp_rhs = bind(qbx,
sym.make_sym_vector("bc", dim) + u_A_sym_bdry)(queue,
bc=bc,
mu=mu,
omega=omega)
gmres_result = gmres(bound_op.scipy_op(queue,
"sigma",
np.float64,
mu=mu,
normal=normal),
bvp_rhs,
x0=bvp_rhs,
tol=1e-9,
progress=True,
stall_iterations=0,
hard_failure=True)
# }}}
# {{{ postprocess/visualize
sigma = gmres_result.solution
sigma_int_val_sym = sym.make_sym_vector("sigma_int_val", 2)
int_val = bind(qbx, sym.integral(2, 1, sigma_sym))(queue, sigma=sigma)
int_val = -int_val / (2 * np.pi)
print("int_val = ", int_val)
u_A_sym_vol = stokeslet_obj.apply( # noqa: N806
omega_sym, mu_sym, qbx_forced_limit=2)
representation_sym = (
-stresslet_obj.apply(sigma_sym, nvec_sym, mu_sym, qbx_forced_limit=2) +
stokeslet_obj.apply(meanless_sigma_sym, mu_sym, qbx_forced_limit=2) -
u_A_sym_vol + sigma_int_val_sym)
nsamp = 30
eval_points_1d = np.linspace(-3., 3., nsamp)
eval_points = np.zeros((2, len(eval_points_1d)**2))
eval_points[0, :] = np.tile(eval_points_1d, len(eval_points_1d))
eval_points[1, :] = np.repeat(eval_points_1d, len(eval_points_1d))
def circle_mask(test_points, radius):
return (test_points[0, :]**2 + test_points[1, :]**2 > radius**2)
def outside_circle(test_points, radius):
mask = circle_mask(test_points, radius)
return np.array([row[mask] for row in test_points])
eval_points = outside_circle(eval_points, radius=circle_rad)
from pytential.target import PointsTarget
vel = bind((qbx, PointsTarget(eval_points)),
representation_sym)(queue,
sigma=sigma,
mu=mu,
normal=normal,
sigma_int_val=int_val,
omega=omega)
print("@@@@@@@@")
fplot = FieldPlotter(np.zeros(2), extent=6, npoints=100)
plot_pts = outside_circle(fplot.points, radius=circle_rad)
plot_vel = bind((qbx, PointsTarget(plot_pts)),
representation_sym)(queue,
sigma=sigma,
mu=mu,
normal=normal,
sigma_int_val=int_val,
omega=omega)
def get_obj_array(obj_array):
return make_obj_array([ary.get() for ary in obj_array])
exact_soln = fund_and_rot_soln(cl.array.to_device(queue, eval_points[0]),
cl.array.to_device(queue, eval_points[1]),
fund_soln_loc, strength)
vel = get_obj_array(vel)
err = vel - get_obj_array(exact_soln)
# FIXME: Pointwise relative errors don't make sense!
rel_err = err / (get_obj_array(exact_soln))
if 0:
print("@@@@@@@@")
print("vel[0], err[0], rel_err[0] ***** vel[1], err[1], rel_err[1]: ")
for i in range(len(vel[0])):
print("%15.8e, %15.8e, %15.8e ***** %15.8e, %15.8e, %15.8e\n" %
(vel[0][i], err[0][i], rel_err[0][i], vel[1][i], err[1][i],
rel_err[1][i]))
print("@@@@@@@@")
l2_err = np.sqrt((6. / (nsamp - 1))**2 * np.sum(err[0] * err[0]) +
(6. / (nsamp - 1))**2 * np.sum(err[1] * err[1]))
l2_rel_err = np.sqrt((6. /
(nsamp - 1))**2 * np.sum(rel_err[0] * rel_err[0]) +
(6. /
(nsamp - 1))**2 * np.sum(rel_err[1] * rel_err[1]))
print("L2 error estimate: ", l2_err)
print("L2 rel error estimate: ", l2_rel_err)
print("max error at sampled points: ", max(abs(err[0])), max(abs(err[1])))
print("max rel error at sampled points: ", max(abs(rel_err[0])),
max(abs(rel_err[1])))
if do_plot:
import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
full_pot = np.zeros_like(fplot.points) * float("nan")
mask = circle_mask(fplot.points, radius=circle_rad)
for i, vel in enumerate(plot_vel):
full_pot[i, mask] = vel.get()
plt.quiver(fplot.points[0],
fplot.points[1],
full_pot[0],
full_pot[1],
linewidth=0.1)
plt.savefig("exterior-2d-field.pdf")
# }}}
h_max = bind(qbx, sym.h_max(qbx.ambient_dim))(queue)
return h_max, l2_err
def Wr(operand: sym.Expression) -> sym.Expression: # noqa: N802
return sym.Ones() * sym.integral(self.ambient_dim, self.dim,
operand)
def run_exterior_stokes(
ctx_factory,
*,
ambient_dim,
target_order,
qbx_order,
resolution,
fmm_order=False, # FIXME: FMM is slower than direct evaluation
source_ovsmp=None,
radius=1.5,
mu=1.0,
visualize=False,
_target_association_tolerance=0.05,
_expansions_in_tree_have_extent=True):
cl_ctx = cl.create_some_context()
queue = cl.CommandQueue(cl_ctx)
actx = PyOpenCLArrayContext(queue)
# {{{ geometry
if source_ovsmp is None:
source_ovsmp = 4 if ambient_dim == 2 else 8
places = {}
if ambient_dim == 2:
from meshmode.mesh.generation import make_curve_mesh, ellipse
mesh = make_curve_mesh(lambda t: radius * ellipse(1.0, t),
np.linspace(0.0, 1.0, resolution + 1),
target_order)
elif ambient_dim == 3:
from meshmode.mesh.generation import generate_icosphere
mesh = generate_icosphere(radius,
target_order + 1,
uniform_refinement_rounds=resolution)
else:
raise ValueError(f"unsupported dimension: {ambient_dim}")
pre_density_discr = Discretization(
actx, mesh, InterpolatoryQuadratureSimplexGroupFactory(target_order))
from pytential.qbx import QBXLayerPotentialSource
qbx = QBXLayerPotentialSource(
pre_density_discr,
fine_order=source_ovsmp * target_order,
qbx_order=qbx_order,
fmm_order=fmm_order,
target_association_tolerance=_target_association_tolerance,
_expansions_in_tree_have_extent=_expansions_in_tree_have_extent)
places["source"] = qbx
from extra_int_eq_data import make_source_and_target_points
point_source, point_target = make_source_and_target_points(
side=+1,
inner_radius=0.5 * radius,
outer_radius=2.0 * radius,
ambient_dim=ambient_dim,
)
places["point_source"] = point_source
places["point_target"] = point_target
if visualize:
from sumpy.visualization import make_field_plotter_from_bbox
from meshmode.mesh.processing import find_bounding_box
fplot = make_field_plotter_from_bbox(find_bounding_box(mesh),
h=0.1,
extend_factor=1.0)
mask = np.linalg.norm(fplot.points, ord=2, axis=0) > (radius + 0.25)
from pytential.target import PointsTarget
plot_target = PointsTarget(fplot.points[:, mask].copy())
places["plot_target"] = plot_target
del mask
places = GeometryCollection(places, auto_where="source")
density_discr = places.get_discretization("source")
logger.info("ndofs: %d", density_discr.ndofs)
logger.info("nelements: %d", density_discr.mesh.nelements)
# }}}
# {{{ symbolic
sym_normal = sym.make_sym_vector("normal", ambient_dim)
sym_mu = sym.var("mu")
if ambient_dim == 2:
from pytential.symbolic.stokes import HsiaoKressExteriorStokesOperator
sym_omega = sym.make_sym_vector("omega", ambient_dim)
op = HsiaoKressExteriorStokesOperator(omega=sym_omega)
elif ambient_dim == 3:
from pytential.symbolic.stokes import HebekerExteriorStokesOperator
op = HebekerExteriorStokesOperator()
else:
assert False
sym_sigma = op.get_density_var("sigma")
sym_bc = op.get_density_var("bc")
sym_op = op.operator(sym_sigma, normal=sym_normal, mu=sym_mu)
sym_rhs = op.prepare_rhs(sym_bc, mu=mu)
sym_velocity = op.velocity(sym_sigma, normal=sym_normal, mu=sym_mu)
sym_source_pot = op.stokeslet.apply(sym_sigma,
sym_mu,
qbx_forced_limit=None)
# }}}
# {{{ boundary conditions
normal = bind(places, sym.normal(ambient_dim).as_vector())(actx)
np.random.seed(42)
charges = make_obj_array([
actx.from_numpy(np.random.randn(point_source.ndofs))
for _ in range(ambient_dim)
])
if ambient_dim == 2:
total_charge = make_obj_array([actx.np.sum(c) for c in charges])
omega = bind(places, total_charge * sym.Ones())(actx)
if ambient_dim == 2:
bc_context = {"mu": mu, "omega": omega}
op_context = {"mu": mu, "omega": omega, "normal": normal}
else:
bc_context = {}
op_context = {"mu": mu, "normal": normal}
bc = bind(places, sym_source_pot,
auto_where=("point_source", "source"))(actx,
sigma=charges,
mu=mu)
rhs = bind(places, sym_rhs)(actx, bc=bc, **bc_context)
bound_op = bind(places, sym_op)
# }}}
# {{{ solve
from pytential.solve import gmres
gmres_tol = 1.0e-9
result = gmres(bound_op.scipy_op(actx, "sigma", np.float64, **op_context),
rhs,
x0=rhs,
tol=gmres_tol,
progress=visualize,
stall_iterations=0,
hard_failure=True)
sigma = result.solution
# }}}
# {{{ check velocity at "point_target"
def rnorm2(x, y):
y_norm = actx.np.linalg.norm(y.dot(y), ord=2)
if y_norm < 1.0e-14:
y_norm = 1.0
d = x - y
return actx.np.linalg.norm(d.dot(d), ord=2) / y_norm
ps_velocity = bind(places,
sym_velocity,
auto_where=("source", "point_target"))(actx,
sigma=sigma,
**op_context)
ex_velocity = bind(places,
sym_source_pot,
auto_where=("point_source",
"point_target"))(actx, sigma=charges, mu=mu)
v_error = rnorm2(ps_velocity, ex_velocity)
h_max = bind(places, sym.h_max(ambient_dim))(actx)
logger.info("resolution %4d h_max %.5e error %.5e", resolution, h_max,
v_error)
# }}}}
# {{{ visualize
if not visualize:
return h_max, v_error
from meshmode.discretization.visualization import make_visualizer
vis = make_visualizer(actx, density_discr, target_order)
filename = "stokes_solution_{}d_{}_ovsmp_{}.vtu".format(
ambient_dim, resolution, source_ovsmp)
vis.write_vtk_file(filename, [
("density", sigma),
("bc", bc),
("rhs", rhs),
],
overwrite=True)
# }}}
return h_max, v_error
def ref_result(self):
return make_obj_array([1.0e-15 * sym.Ones()] * self.ambient_dim)