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MathGroup Archive 2006

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69165] Unexpected "Invalid comparison" error when plotting function defined with a Condition pattern
  • From: "Andrew Moylan" <andrew.j.moylan at gmail.com>
  • Date: Thu, 31 Aug 2006 04:39:48 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

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


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