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MathGroup Archive 2004

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Re: Problem with transformation rules in Plot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg48510] Re: Problem with transformation rules in Plot
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 4 Jun 2004 04:49:24 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <c9k462$fho$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

and

Plot[Evaluate[{f[x],g[x]}/.{a->1}] , {x,0,1}]

will work, because Plot[] has te attribute HoldAll

Regards
  Jens

Alain Cochard wrote:
> 
> Hello.  I would be grateful if someone could explain to me the
> following behavior (i.e., is it normal? why?), or point me to a
> relevant part of a manual:
> 
> Mathematica 4.0 for Linux
> Copyright 1988-1999 Wolfram Research, Inc.
>  -- Motif graphics initialized --
> 
> In[1]:= f[x_]:=a x ; g[x_]:=2 a x ;
> 
> In[2]:= Plot[ f[x]/.{a->1} , {x,0,1}]  (* Fine *)
> 
> Out[2]= -Graphics-
> 
> In[3]:= {f[x],g[x]}/.{a->1}
> 
> Out[3]= {x, 2 x}  (* Fine, just checking *)
> 
> In[4]:= Plot[{f[x],g[x]}/.{a->1} , {x,0,1}]
> 
> Plot::plnr: {f[x], g[x]} /. {a -> 1} is not a machine-size real number at x =
>               -8
>     4.16667 10  .
> 
> Plot::plnr: {f[x], g[x]} /. {a -> 1} is not a machine-size real number at x =
>     0.040567.
> 
> Plot::plnr: {f[x], g[x]} /. {a -> 1} is not a machine-size real number at x =
>     0.0848088.
> 
> General::stop: Further output of Plot::plnr
>      will be suppressed during this calculation.
> 
> Out[4]= -Graphics-
> 
> (* So the question is: why does it work for f[x] alone, and not for
> f[x] and g[x]? *)
> 
> (* The following works fine, but is there a better workaround? *)
> 
> In[5]:= data={a->1} ; Plot[{ f[x]/.data , g[x]/.data }, {x,0,1}]
> 
> Many thanks in advance,
> Alain Cochard


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