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Re: Don't understand Plot behavior
*To*: mathgroup at smc.vnet.net
*Subject*: [mg39993] Re: Don't understand Plot behavior
*From*: bobhanlon at aol.com (Bob Hanlon)
*Date*: Fri, 14 Mar 2003 04:45:28 -0500 (EST)
*References*: <b4pf6u$bu4$1@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
f[t_]:= D[t , t];
The Evaluate is needed to override Plot's attribute of HoldAll. If you bury
the Evaluate inside a List then the first argument is not evaluated. You need
to Evaluate the the first argument, that is, the List.
Plot[Evaluate[{f[t],0}],{t,0,1}];
or define f with
f[t_]:=Evaluate[D[t,t]];
Plot[{f[t],0},{t,0,1}];
Bob Hanlon
In article <b4pf6u$bu4$1 at smc.vnet.net>, Alain Cochard <al2 at noos.fr> wrote:
<<
Subject: Don't understand Plot behavior
From: Alain Cochard <al2 at noos.fr>
To: mathgroup at smc.vnet.net
Date: Thu, 13 Mar 2003 08:23:58 +0000 (UTC)
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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