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MathGroup Archive 2003

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Re: Re: Don't understand Plot behavior

  • To: mathgroup at smc.vnet.net
  • Subject: [mg40021] Re: [mg39995] Re: Don't understand Plot behavior
  • From: Dr Bob <drbob at bigfoot.com>
  • Date: Sun, 16 Mar 2003 02:21:35 -0500 (EST)
  • References: <b4pf6u$bu4$1@smc.vnet.net> <200303140945.EAA18797@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

It has nothing to do with what Evaluate is wrapped around.  From Help:

"Evaluate only overrides HoldFirst, etc. attributes when it appears 
directly as the head of the function argument that would otherwise be 
held."

Plot has attribute HoldAll, and List does not.

Bobby

On Fri, 14 Mar 2003 04:45:35 -0500 (EST), Jens-Peer Kuska 
<kuska at informatik.uni-leipzig.de> wrote:

> Hi,
>
> yes because Evaluate[] work only if it is
> waraped arround a function argument or a
> sequence of arguments, and you have to write
>
> Plot[Evaluate[{f[t],0}] , {t, 0, 1}]
>
> otherwise the List[] argument is evaluatet that
> help Plot[] nothing.
>
> Regards
> Jens
>
> Alain Cochard wrote:
>>
>> In[1]:= f[t_]:= D[t  , t]
>>
>> In[2]:= Plot[Evaluate[f[t]] , {t, 0, 1}]
>>
>> Out[2]= -Graphics- [The plot is fine]
>>
>> In[3]:= Plot[{Evaluate[f[t]],0} , {t, 0, 1}]
>>
>> -8
>> General::ivar: 4.16667 10   is not a valid variable.
>>
>> [...]
>>
>> General::stop: Further output of General::ivar
>> will be suppressed during this calculation.
>>
>> Plot::plnr: Evaluate[f[t]] is not a machine-size real number at t =
>> -8
>> 4.16667 10  .
>>
>> [...]
>>
>> General::stop: Further output of Plot::plnr
>> will be suppressed during this calculation.
>>
>> Out[3]= -Graphics-[The plot just shows the axes]
>>
>> In[4]:= harhar=Evaluate[f[t]]; Plot[{harhar,0} , {t, 0, 1}]
>>
>> Out[4]= -Graphics-[The plot is fine]
>>
>> In[5]:= $Version
>>
>> Out[5]= 4.1 for Sun Solaris (November 8, 2000)
>>
>> Is this behavior normal?  Thx in advance.
>>
>> Alain Cochard
>> al2 at noos.fr
>
>



-- 
majort at cox-internet.com
Bobby R. Treat



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