# Tag Info

If you want to use the coefficient of the form $$\alpha = \begin{cases} \alpha_1 & r < 0.5 \\ \alpha_2 & r > 0.5 \end{cases}$$ it is useful to work in polar coordinates. You build two pieces of the solution $$u_1(r,\theta), \qquad r < 0.5$$ and $$u_2(r,\theta), \qquad r > 0.5$$ Then at the interface you ensure solution and flux ...