pubs: Fellwalker - HOP also claims to be insensitive to parameter set…

…tings

so it's not suprising that FellWalker is also insensitive to parameter
settings.

pubs/fellwalker/fellwalker.tex

@@ -226,7 +226,10 @@ \section{Introduction}
 minimum). It shares much in common with the HOP algorithm
 \citep{1998Eisenstein} - another gradient-tracing watershed algorithm, but is
 designed for use with gridded observational data rather than particles in
-an N-body simulation.
+an N-body simulation. HOP is known to be relatively insensitive to the
+values supplied for its parameters (except the lower threshold),
+reflecting a similar feature found for FellWalker (see
+section~\ref{sec:compare}).
 
 An implementation of the FellWalker algorithm is included in the Starlink
 \htmladdnormallinkfoot{CUPID}{http://starlink.jach.hawaii.edu/starlink/CUPID}