Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2009

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

Search the Archive

Re: Not all points plot on my graph...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg105206] Re: Not all points plot on my graph...
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Tue, 24 Nov 2009 05:49:39 -0500 (EST)

On 11/23/09 at 6:49 AM, davidfrick2003 at yahoo.com (davef) wrote:

>Why is it when I write this...

>Clear[f, x]
>f[x_] = (x + 2)^(2/3)
>Plot[f[x], {x, -3, 0}, PlotRange -> {{-3, 0}, {-4, 4}}]
>f[-3]

>.. I get no values show in the graph for x<-2 even though f[-3]
>evaluates to (-1)^(2/3).

>(-1)^(2/3) evaluates as f[-3]=1 so why wouldn't the point (-3,1)
>plot on my graph?

When you say f[-3] evaluates to 1, did you actually evaluate
this with Mathematica or in your head? On my system

In[6]:= f[-3] // N

Out[6]= -0.5+0.866025 I

That is Mathematica is not evaluating f[-3] to 1 as you suggest
which explains the missing points. Mathematica by default is not
restricted to real solutions nor does Mathematica give priority
to a real over a complex solution when both exist.



  • Prev by Date: Re: Not all points plot on my graph...
  • Next by Date: Re: Importing fonts into Inkscape
  • Previous by thread: Re: Not all points plot on my graph...
  • Next by thread: Re: Not all points plot on my graph...