Alternate evans functions and viscous shock waves

The Evans function is known as a helpful tool for locating the spectrum of some variational differential operators. This is of special interest regard ing the stability analysis of traveling waves, such as reaction-diffusion w aves, solitary waves, viscous shock waves, etc., and has been used in numer ous contexts. The rst aim of this paper is to present an overview of the va rious ways to de ne an Evans function for an abstract differential operator . Not all of these alternatives are new, but we show consistent connections between them. Subsequently, we focus on viscous shock waves, extending the work of Gardner and Zumbrun in several directions. In particular, we (i) s how some advantages of alternate Evans functions in practical computations, ( i) carry out a refined analysis in case of neutral stability, and (iii) show how to treat systems of size n>2, thus resolving a problem left open b y Gardner and Zumbrun.