degenerate parabolic PDE and pdepe

Hi,

i hope someone can help me on that topic:

Given a 1 dimensional problem pdepe is what i considered to be the best choice. But my PDE changes at a certain point from second order to first order type.

that would mean the flux term consists of two parts:

f=r+b*du/dx

and b will become zero at a certain solution u

can pdepe handle that ?

Thank you