我用第一个子域中的斯托克斯方程和第二个子域中的混合泊松方程（达西）创建了一个划分域。我使用 UnitSquare，子域 1 应该是从 0 到 0,5 的区间，子域 2 应该是从 0,5 到 1 的区间。
但现在我收到以下错误：
解决线性变分问题。与调用 numeric 相关的 UMFPACK 问题 * 警告：UMFPACK 报告正在求解的矩阵是奇异的。与调用求解有关的 UMFPACK 问题 *警告：UMFPACK 报告正在求解的矩阵是奇异的。断言 vmax>=vmin, "空范围，请指定 vmin 和/或 vmax" 断言错误：空范围，请指定 vmin 和/或 vmax
任何人都可以帮忙吗？谢谢！
这是代码：
enter code here
#-*- coding: utf-8 -*-
from dolfin import *
import numpy as np
# Define mesh
mesh = UnitSquare(32,32)
#Subdomain 1
# Gitter übergeben
subdomains = CellFunction("uint", mesh)
# Klasse des Teilgebiets
class Domain_1(SubDomain):
def inside(self, x, on_boundary):
return between(x[0], (0, 0.5)) # Koordinatenangabe des Teilgebiets
# Objekt der Klasse erstellen
sub_domain1 = Domain_1()
sub_domain1.mark(subdomains,0)
# Definition Funktionenräume
U = FunctionSpace(mesh, "CG", 2)
V = FunctionSpace(mesh, "CG", 1)
W = U*V
# Definition Trial- und Testfunktion
(u, p) = TrialFunctions(W)
(v, q) = TestFunctions(W)
# boundary condition
p_in = 1
p_out = 0
noslip = DirichletBC(W.sub(0), (0),
"on_boundary && \
(x[1] <= DOLFIN_EPS | x[1] >= 0.5-DOLFIN_EPS)")
inflow = DirichletBC(W.sub(1), p_in, "x[0] <= 0.0 + DOLFIN_EPS*1000")
outflow = DirichletBC(W.sub(1), p_out, "x[0] >= 0.5 - DOLFIN_EPS*1000")
bcp = [noslip,inflow, outflow]
# Definition f
f = Expression("0")
# Variationsformulierung
a = inner(grad(u), grad(v))*dx + div(v)*p*dx(0) + q*div(u)*dx(0)
L = inner(f,v)*dx(0)
# Lösung berechnen
w = Function(W)
problem = LinearVariationalProblem(a, L, w, bcp)
solver = LinearVariationalSolver(problem)
solver.solve()
(u, p) = w.split()
# Subdomain 2
# Gitter übergeben
subdomains = CellFunction("uint", mesh)
# Klasse des Teilgebiets
class Domain_2(SubDomain):
def inside(self,x,on_boundary):
return between(x[0], (0.5,1.0)) # Koordinatenangabe des Teilgebiets
# Objekt der Klasse erstellen
sub_domain2 = Domain_2()
sub_domain2.mark(subdomains,1)
# Define function spaces and mixed (product) space
BDM = FunctionSpace(mesh, "BDM", 1)
DG = FunctionSpace(mesh, "DG", 0)
CG = FunctionSpace(mesh, "CG", 1)
W = MixedFunctionSpace([BDM, DG, CG])
# Define trial and test functions
(sigma, u, p) = TrialFunctions(W)
(tau, v, q) = TestFunctions(W)
#Define pressure boundary condition
p_in = 1
p_out = 0
noslip = DirichletBC(W.sub(1), (0),
"on_boundary && \
(x[1] <= 0.5 + DOLFIN_EPS | x[1] >= 1.0-DOLFIN_EPS)")
inflow = DirichletBC(W.sub(2), p_in, "x[0] <= 0.5 + DOLFIN_EPS*1000")
outflow = DirichletBC(W.sub(2), p_out, "x[0] >= 1.0 - DOLFIN_EPS*1000")
bcp = [noslip,inflow, outflow]
# Define f
#f = Expression("0")
f = Expression("10*exp(-(pow(x[0] - 0.5, 2) + pow(x[1] - 0.5, 2)) / 0.02)")
# Define variational form
a = (dot(sigma, tau) + div(tau)*u + div(sigma)*v)*dx(1) + inner(p,q)*dx(1) + u*q*dx(1)
L = f*v*dx(1)
# Compute solution
w = Function(W)
problem = LinearVariationalProblem(a, L, w, bcp)
solver = LinearVariationalSolver(problem)
solver.solve()
(sigma, u, p) = w.split()
# plot
plot(u, axes = True, interactive=True, title = "u")
plot(p, axes = True, interactive=True, title = "p")
我忘记了这个术语中的 dx(0)。但这不是问题所在。
在代码的第一部分（Stokes）中，我尝试用以下方式编写无滑移条件：
# Randbedingungen
def top_bottom(x, on_boundary):
return x[1] > 1.0 - DOLFIN_EPS or x[1] < DOLFIN_EPS
noslip = Constant((0.0,0.0))
bc0 = DirichletBC(W.sub(0), noslip, top_bottom)
p_in = 1
p_out = 0
inflow = DirichletBC(W.sub(1), p_in, "x[0] <= 0.0 + DOLFIN_EPS*1000")
outflow = DirichletBC(W.sub(1), p_out, "x[0] >= 0.5 - DOLFIN_EPS*1000")
bcp = [bc0, inflow, outflow]
# Definition f
f = Expression("(0.0, 0.0)")
# Variationsformulierung Stokes
a = inner(grad(u), grad(v))*dx(0) + div(v)*p*dx(0) + q*div(u)*dx(0)
L = inner(f,v)*dx(0)
但现在我收到以下错误：
Shape mismatch: line 56, in <module> L = inner(f,v)*dx(0
任何人都可以帮忙吗？谢谢！