Well-posedness of sudden directional diffusion equations

Abstract

Our goal is to establish existence with suitable initial data of solutions to general parabolic equation in one dimension, $u_t = L(u_x)_x$, where $L$ is merely a monotone function. We also expose the basic properties of solutions, concentrating on maximal possible regularity. Analysis of solutions with convex initial data explains why we may call them {\it almost classical}. Some qualitative aspects of solutions, like facets -- flat regions of solutions, are studied too.