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

• To: mathgroup at smc.vnet.net
• Subject: [mg69175] Re: Unexpected "Invalid comparison" error when plotting function defined with a Condition pattern
• From: "Jens-Peer Kuska" <kuska at informatik.uni-leipzig.de>
• Date: Fri, 1 Sep 2006 06:40:24 -0400 (EDT)
• Organization: Uni Leipzig
• References: <ed68td$jgk$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

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

"Andrew Moylan" <andrew.j.moylan at gmail.com> 
schrieb im Newsbeitrag 
news:ed68td$jgk$1 at smc.vnet.net...
| Hi,
|
| Please consider the following simple function, 
defined for positive x
| using a Condition pattern:
|
|  g[x_ /; 0 < x] = x;
|
| When I try to plot this function in the 
following way:
|
|  Plot[Abs[g[10^y]], {y, 1, 2}];
|
| I unexpectedly receive some "Less::nord : 
Invalid comparison with 10. +
| 0. I attempted" errors. Can anyone explain why 
this is, and how I
| should best prevent it?
|
| Relevant note:
| Both of the following different plots of g 
succeed with no errors:
|  Plot[Abs[g[y]], {y, 1, 2}];
|  Plot[g[10^y], {y, 1, 2}];
|
| Irrelevant note:
| In my actual application, the function g is more 
complicated and is
| complex-valued (hence my use of Abs); but the 
error is reproducable
| with the very simple real-valued function g as 
defined above.
|
| Thanks for any insight you might be able to give 
me on this.
|
| Cheers,
|
| Andrew
|