Setting

Equation

Boundary condition

Selection rule

Set I

Poisson

f(x,y) = 1

Dirichlet

u = 0

MAX

Set II

Laplace

f(x,y) = 0

Dirichlet

u = 1

MIN

Set III

Poisson

f(x,y) = 1

Neumann

∂u/∂n = 0

MAX