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MathGroup Archive 2000

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Re: Plots with Variable Limits?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24112] Re: Plots with Variable Limits?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 28 Jun 2000 02:11:37 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <8j9djn$51e@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

Plot[] has the hold all attribute. And

Plot[ f[r,a], {x,-2a,2a} ]  /.  a->10

will evaluate 

Plot[ f[r,a], {x,-2a,2a} ] 

ans see that it can't draw the it because a is unknown.
Than it replaces a with 10 and can draw it, so the plot 
is gernerated. You must preven the first evaluation with


ReleaseHold @ (Hold[Plot[f[r, a], Evaluate[{r, -2a, 2a}]]] /. a -> 10)

and all works fine.

Regards
  Jens


"A. E. Siegman" 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


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