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