MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Plotting f = Function[x,expr] and f[x_] := expr

  • To: mathgroup at smc.vnet.net
  • Subject: [mg92425] Re: Plotting f = Function[x,expr] and f[x_] := expr
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Tue, 30 Sep 2008 21:50:32 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <gbt2oo$lbo$1@smc.vnet.net>

E. Martin-Serrano wrote:
> Hi,
> 
> Why this apparent estrange behavior while plotting  functions  under the
> formats f[x_] := -20 x^3 + 3 x^5 and f = Function[x, -20 x^3 + 3 x^5]?, 
> 
> In particular  the second derivative f ''[x]  for -20 x^3 + 3 x^5 fails to
> render the shame shape in following examples . Please, see below: 

FWIW, to me as well as for Mathematica 6.0.3 on 64-bit Intal Mac OS X 
10.5.5, the plots are identical in each case.

   In[123]:=

     Clear[f, x]
     f[x_] := -20 x^3 + 3 x^5
     pp1 = Plot[f[x], {x, -2 Pi, 2 Pi}, PlotStyle -> Red]
     pp2 = Plot[f'[x], {x, -2 Pi, 2 Pi}, PlotStyle -> Green]
     pp3 = Plot[f''[x], {x, -2 Pi, 2 Pi}, PlotStyle -> Blue]
     pp4 = Plot[{f[x], f'[x], f''[x]}, {x, -2 Pi, 2 Pi},
       PlotStyle -> {Red, Green, Blue},
       PlotRange -> {{-6.28318, 6.27681}, {-14129, 14084}}]

     Clear[f, x]
     f = Function[x, -20 x^3 + 3 x^5];
     p1 = Plot[f[x], {x, -2 Pi, 2 Pi}, PlotStyle -> Red]
     p2 = Plot[f'[x], {x, -2 Pi, 2 Pi}, PlotStyle -> Green]
     p3 = Plot[f''[x], {x, -2 Pi, 2 Pi}, PlotStyle -> Blue]
     p4 = Plot[{f[x], f'[x], f''[x]}, {x, -2 Pi, 2 Pi},
       PlotStyle -> {Red, Green, Blue},
       PlotRange -> {{-6.28318, 6.27681}, {-14129, 14084}}]

     p1 === pp1
     p2 === pp2
     p3 === pp3
     p4 === pp4


   Out[135]= True

   Out[136]= True

   Out[137]= True

   Out[138]= True

   In[139]:= $Version

   Out[139]= "6.0 for Mac OS X x86 (64-bit) (May 21, 2008)"

Regards,
-- Jean-Marc


  • Prev by Date: Re: Display Math Formula
  • Next by Date: Re: Redirecting input
  • Previous by thread: Plotting f = Function[x,expr] and f[x_] := expr
  • Next by thread: Re: Plotting f = Function[x,expr] and f[x_] := expr