def convergence(nrefine=5):
err, h = numpy.array([main(nr=irefine) for irefine in log.range('refine', nrefine)]).T
with plot.PyPlot( 'convergence' ) as plt:
plt.loglog(h, err, 'k*--')
plt.slope_triangle(h, err)
plt.ylabel('L2 error of stress')
plt.grid(True)
def newton(f, x0, maxiter, restol, lintol):
'''find x such that f(x) = 0, starting at x0'''
for i in log.range('newton', maxiter + 1):
if i > 0:
# solve system linearised around `x`, solution in `direction`
J = f(x, jacobian=True)
direction = -J.solve(residual, tol=lintol)
xprev = x
residual_norm_prev = residual_norm
# line search, stop if there is convergence w.r.t. iteration `i-1`
for j in range(4):
x = xprev + (0.5)**j * direction
residual = f(x)
residual_norm = numpy.linalg.norm(residual, 2)
if residual_norm < residual_norm_prev:
break
# else: no convergence, repeat and reduce step size by one half
else:
log.warning('divergence')
else:
# before first iteration, compute initial residual
x = x0
residual = f(x)
residual_norm = numpy.linalg.norm(residual, 2)
log.info('residual norm: {:.5e}'.format(residual_norm))
if residual_norm < restol:
break
else:
raise ValueError(
'newton did not converge in {} iterations'.format(maxiter))
return x
def main(alpha=0.01, nelems=64, degree=2, dt=0.01, tend=1):
# construct topology, geometry and basis
verts = numpy.linspace(0, 1, nelems + 1)
domain, geom = mesh.rectilinear([verts, verts])
basis = domain.basis('spline', degree=degree)
ischeme = 'gauss4'
print(basis)
exit()
# construct matrices
A = 1 / dt * basis['i'] * basis['j'] + alpha / 2 * basis['i,k'] * basis[
'j,k']
B = 1 / dt * basis['i'] * basis['j'] - alpha / 2 * basis['i,k'] * basis[
'j,k']
A, B = domain.integrate([A, B], geometry=geom, ischeme=ischeme)
# construct dirichlet boundary constraints
cons = domain.boundary.project(0,
onto=basis,
geometry=geom,
ischeme=ischeme)
# construct initial condition
x0, x1 = geom
l = function.max(
# level set of a square centred at (0.3,0.4)
0.15 - (abs(0.3 - x0) + abs(0.4 - x1)),
# level set of a circle centred at (0.7,0.6)
0.15 - ((0.7 - x0)**2 + (0.6 - x1)**2)**0.5,
)
# smooth heaviside of level set
u0 = 0.5 + 0.5 * function.tanh(nelems / 2 * l)
for n in log.range('timestep', round(tend / dt) + 1):
if n == 0:
# project initial condition on `basis`
w = domain.project(u0, onto=basis, geometry=geom, ischeme=ischeme)
else:
# time step
w = A.solve(B.matvec(w), constrain=cons)
# construct solution
u = basis.dot(w)
# plot
points, colors = domain.elem_eval([geom, u],
ischeme='bezier3',
separate=True)
with plot.PyPlot('temperature') as plt:
plt.title('t={:5.2f}'.format(n * dt))
plt.mesh(points, colors)
plt.colorbar()
plt.clim(0, 1)
def convergence(nrefine=5):
err = []
h = []
for irefine in log.range('refine', nrefine):
serr, hmax = main(nr=irefine)
err.append(serr)
h.append(hmax)
with plot.PyPlot('convergence') as plt:
plt.loglog(h, err, 'k*--')
plt.slope_triangle(h, err)
plt.ylabel('L2 error of stress')
plt.grid(True)
def main(nelems=8, degree=2, diffusion_over_h=0.5):
# construct geometry and initial topology
verts = numpy.linspace(0, 1, nelems + 1)
domain, geom = mesh.rectilinear([verts, verts])
# common integration arguments
int_kwargs = dict(geometry=geom, ischeme='gauss{}'.format(degree * 2 + 1))
for i in log.range('refinement', 4):
# create domain and basis for global refinement step `i`
if i > 0:
domain = domain.refined
φ = domain.basis('spline', degree=degree)
# compute an initial guess based on the previous iteration, if any
if i > 0:
u_hat = domain.project(u, onto=φ, **int_kwargs)
else:
u_hat = numpy.zeros(φ.shape)
# solve
R = functools.partial(residual,
diffusion=diffusion_over_h / (nelems * 2**i),
geom=geom,
domain=domain,
φ=φ,
**int_kwargs)
u_hat = newton(R, x0=u_hat, maxiter=20, restol=1e-8, lintol=0)
# expand solution
u = φ.dot(u_hat)
# plot
points, colors = domain.elem_eval([geom, u],
ischeme='bezier3',
separate=True)
with plot.PyPlot('solution') as plt:
plt.title('nelems={}'.format(nelems * 2**i))
plt.mesh(points, colors)
plt.colorbar()
plt.clim(0, 1)
plt.xlabel('t')
plt.ylabel('x')
def convergence(
degree = 2 ,
nrefine = 6,
maxrefine = 7
):
"""Performs convergence study for the example
Parameters
----------
degree : int
b-spline degree
nrefine : int
level of h-refinement
maxrefine : int
bisectioning steps
"""
l2err, h1err, errh = numpy.array([main(nelems=2**(1+irefine), maxrefine = nmaxrefine, degree=degree)[1] for nmaxrefine in range(1,maxrefine+1) for irefine in log.range('refine', nrefine)]).T
h = .5**numpy.arange(nrefine)
clrstr = ['k*--','ks--','k^--','ko--','k--','k+--','kv--','k<--','kX--','k>--']
# ploting errors
with plot.PyPlot('L2error',ndigits=0) as plt:
for m in range(0,maxrefine):
plt.loglog(h, l2err[nrefine*m:nrefine*(m+1)], clrstr[m],label='maxrefine ={}'.format(m))
plt.slope_triangle(h, l2err[nrefine*m:nrefine*(m+1)])
plt.legend()
plt.ylabel('L2 error')
plt.grid(True)
with plot.PyPlot('H1error',ndigits=0) as plt:
for m in range(0,maxrefine):
plt.loglog(h, h1err[nrefine*m:nrefine*(m+1)], clrstr[m],label='maxrefine ={}'.format(m))
plt.slope_triangle(h, h1err[nrefine*m:nrefine*(m+1)])
plt.legend()
plt.ylabel('H1 error')
plt.grid(True)
with plot.PyPlot('Energy_error',ndigits=0) as plt:
for m in range(0,maxrefine):
plt.loglog(h, errh[nrefine*m:nrefine*(m+1)], clrstr[m],label='maxrefine ={}'.format(m))
plt.slope_triangle(h, errh[nrefine*m:nrefine*(m+1)])
plt.legend()
plt.ylabel('Energy error')
plt.grid(True)
def main(
nelems: 'number of elements' = 20,
epsilon: 'epsilon, 0 for automatic (based on nelems)' = 0,
timestep: 'time step' = .01,
maxtime: 'end time' = 1.,
theta: 'contact angle (degrees)' = 90,
init: 'initial condition (random/bubbles)' = 'random',
withplots: 'create plots' = True,
):
mineps = 1. / nelems
if not epsilon:
log.info('setting epsilon=%f' % mineps)
epsilon = mineps
elif epsilon < mineps:
log.warning('epsilon under crititical threshold: %f < %f' %
(epsilon, mineps))
ewall = .5 * numpy.cos(theta * numpy.pi / 180)
# construct mesh
xnodes = ynodes = numpy.linspace(0, 1, nelems + 1)
domain, geom = mesh.rectilinear([xnodes, ynodes])
# prepare bases
cbasis, mubasis = function.chain(
[domain.basis('spline', degree=2),
domain.basis('spline', degree=2)])
# define mixing energy and splitting: F' = f_p - f_n
F = lambda c_: (.5 / epsilon**2) * (c_**2 - 1)**2
f_p = lambda c_: (1. / epsilon**2) * 4 * c_
f_n = lambda c_: (1. / epsilon**2) * (6 * c_ - 2 * c_**3)
# prepare matrix
A = function.outer( cbasis ) \
+ (timestep*epsilon**2) * function.outer( cbasis.grad(geom), mubasis.grad(geom) ).sum(-1) \
+ function.outer( mubasis, mubasis - f_p(cbasis) ) \
- function.outer( mubasis.grad(geom), cbasis.grad(geom) ).sum(-1)
matrix = domain.integrate(A, geometry=geom, ischeme='gauss4')
# prepare wall energy right hand side
rhs0 = domain.boundary.integrate(mubasis * ewall,
geometry=geom,
ischeme='gauss4')
# construct initial condition
if init == 'random':
numpy.random.seed(0)
c = cbasis.dot(numpy.random.normal(0, .5, cbasis.shape))
elif init == 'bubbles':
R1 = .25
R2 = numpy.sqrt(.5) * R1 # area2 = .5 * area1
c = 1 + function.tanh( (R1-function.norm2(geom-(.5+R2/numpy.sqrt(2)+.8*epsilon)))/epsilon ) \
+ function.tanh( (R2-function.norm2(geom-(.5-R1/numpy.sqrt(2)-.8*epsilon)))/epsilon )
else:
raise Exception('unknown init %r' % init)
# prepare plotting
nsteps = numeric.round(maxtime / timestep)
makeplots = MakePlots(domain, geom, nsteps, video=withplots
== 'video') if withplots else lambda *args: None
# start time stepping
for istep in log.range('timestep', nsteps):
Emix = F(c)
Eiface = .5 * (c.grad(geom)**2).sum(-1)
Ewall = (abs(ewall) + ewall * c)
b = cbasis * c - mubasis * f_n(c)
rhs, total, energy_mix, energy_iface = domain.integrate(
[b, c, Emix, Eiface], geometry=geom, ischeme='gauss4')
energy_wall = domain.boundary.integrate(Ewall,
geometry=geom,
ischeme='gauss4')
log.user('concentration {}, energy {}'.format(
total, energy_mix + energy_iface + energy_wall))
lhs = matrix.solve(rhs0 + rhs, tol=1e-12, restart=999)
c = cbasis.dot(lhs)
mu = mubasis.dot(lhs)
makeplots(c, mu, energy_mix, energy_iface, energy_wall)
return lhs, energy_mix, energy_iface, energy_wall
