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RE: Plots with Variable Limits?


> -----Original Message-----
> From:	A. E. Siegman [SMTP:siegman at stanford.edu]
To: mathgroup at smc.vnet.net
> Sent:	Tuesday, June 27, 2000 6:52 AM
> To:	mathgroup at smc.vnet.net
> Subject:	[mg24100] Plots with Variable Limits?
> 
> 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
> 
[Wolf Hartmut]  

You just need to wrap Plot with Unevaluated.

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

This prevents the evaluation of plot _before_ substitution occurs (which
doesn't work  and therefore generates the error message; after the error the
original input was returned which then was replaced and evaluated
correctly).

Kind regards,  Hartmut



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