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MathGroup Archive 2003

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Re: Don't understand Plot behavior

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39994] Re: [mg39971] Don't understand Plot behavior
  • From: Ken Levasseur <klevasseur at mac.com>
  • Date: Fri, 14 Mar 2003 04:45:32 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Alain:

Evaluate needs to be at the top level of the first argument of plot to have
the effect that it has in your first example.

I had defined f=#^2& earlier.

This is what happens in your first example
In[11]:=
Hold[Evaluate[f[t]]]

Out[11]=
Hold[t^2]

Now the second:
In[12]:=
Hold[{Evaluate[f[t]], 0}]

Out[12]=
Hold[{Evaluate[f[t]], 0}]

If you rearrange the the expression, you get what you want:

In[13]:=
Hold[Evaluate[{f[t], 0}]]

Out[13]=
Hold[{t^2, 0}]

Ken Levasseur
UMass Lowell

> From: Alain Cochard <al2 at noos.fr>
To: mathgroup at smc.vnet.net
> Date: Thu, 13 Mar 2003 03:03:58 -0500 (EST)
> To: mathgroup at smc.vnet.net
> Subject: [mg39994] [mg39971] Don't understand Plot behavior
> 
> 
> 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
> 
> 



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