Advection-Diffusion Problem
$$
\left\{
\begin{aligned}
-\alpha \Delta u + \vec{\beta}\cdot \nabla u &= f \quad \text{in } \Omega=[-1,1]\times[-1,1], \\
u &= g \quad \text{on } \partial\Omega,
\end{aligned}
\right.
$$
with source function
and Dirichlet boundary condition