pkg load fem-fenics msh
import_ufl_Problem ('MixedPoisson')

# Create mesh
x = y = linspace (0, 1, 33);
mesh = Mesh(msh2m_structured_mesh (x, y, 1, 1:4));

V = FunctionSpace('MixedPoisson', mesh);

f = Expression ('f', @(x,y) 10*exp(-((x - 0.5)^2 + (y - 0.5)^2) / 0.02));

a = BilinearForm ('MixedPoisson', V);
L = LinearForm ('MixedPoisson', V, f);

# Define essential boundary
bc1 = DirichletBC (SubSpace (V, 1), @(x,y) [0; -sin(5.0*x)], 1);
bc2 = DirichletBC (SubSpace (V, 1), @(x,y) [0;  sin(5.0*x)], 3);

# Compute solution
[A, b] = assemble_system (a, L, bc1, bc2);
sol = A \ b;
func = Function ('func', V, sol);

sigma = Function ('sigma', func, 1);
u = Function ('u', func, 2);

# Plot solution
plot (sigma);
plot (u);