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 >>