Concentration-dependent diffusion. II. Singular problems
when the diffusion coefficient D is a function of the concentration c. Only positive D were considered although we remarked that there are problems of physical interest approximated by D which vanish. Ames [2, Sec. 1.2] discusses a variety of physical situations leading to such problems, as do [3-6]. The ordinary differential equation resulting from the use of the similarity variable t) = x/\/t, mi)+ !! = »■ «