Re: Unexpected "Invalid comparison" error when plotting function defined with a Condition pattern

*To*: mathgroup at smc.vnet.net*Subject*: [mg69238] Re: Unexpected "Invalid comparison" error when plotting function defined with a Condition pattern*From*: Peter Pein <petsie at dordos.net>*Date*: Sun, 3 Sep 2006 01:39:40 -0400 (EDT)*References*: <ed68td$jgk$1@smc.vnet.net> <ed92v5$p46$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Jens-Peer Kuska schrieb: > Hi, > > just read the error message -- 10^y gaves a small > imaginary part and > > g[x_?NumericQ /; 0 < Chop[x]] := x > > will fix the problem. > > Regards > Jens > Hi, it is really not obvious, that 10^y =Exp[y Log[10]] returns an imaginary part for any real y. If one doesn't have this in mind, a sequence of statements like : f[x_?Positive]:=x; f[x_]:=0; Plot[Abs[f[10^y-50]],{y,1,2}] would just "redraw" the x-axis :-( Not only a trap for beginners... Peter