Re: Plots with Variable Limits?
- To: mathgroup at smc.vnet.net
- Subject: [mg24114] Re: [mg24100] Plots with Variable Limits?
- From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
- Date: Wed, 28 Jun 2000 02:11:38 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
on 6/27/00 1:51 PM, A. E. Siegman at siegman at stanford.edu wrote:
> I want to make a test plot of a function f[x,a] versus x for some
> trial value of the parameter a without fixing that parameter for
> subsequent cells, e.g. something like
>
> Plot[ f[r,a], {x,-2a,2a} ] /. a->10
>
> If I try this, Mathematica gives me a "Plot::plln" error -- but then
> goes ahead and makes the correct plot anyway.
>
> I can of course turn off the error -- but what's a better, but still
> clean and simple, way to accomplish this.
>
> Thanks siegman at stanford.edu
>
The problem is that ReplaceAll (which is the same thing as /. ) evaluates
its arguments. That means that Mathematica tries to make a plot before a
gets the value 10, fails and issues the error message. It then returns Plot[
f[r,a], {x,-2a,2a} ] to ReplaceAll[ ,a->10], which then evaluetes correctly.
The simplest wait to avoid the problem is to use:
Unevaluated[Plot[ x^a, {x, -2a, 2a} ] ] /. a -> 10
Andrzej
--
Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/
http://sigma.tuins.ac.jp/