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MathGroup Archive 2006

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Re: machine precision in plot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg65791] Re: machine precision in plot
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Mon, 17 Apr 2006 02:28:48 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <e1suk1$ccp$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Joerg Schaber wrote:
> [This post has been delayed due to email problems - moderator]
> 
> 
> Hi,
> 
> I have defined a function that takes as arguments small values and also 
> returns small values:
> 
> In[237]:=
> P1[7.5`*^-17]
> 
> Out[237]=
> -2.1926`*^7
> 
> However, when plotting the function with
> Plot[P1[x], {x, 5.85`*^-17, 7.15`*^-17}]
> I get an error message:
> Plot::"plld" Endpoints for x in {x, 5.85`*^-17, 7.15`*^-17} must have 
> distinct machine-precision numerical values.
> 
> I thought Mathematica can handle such small numbers.
> Any hint?
> 
> best,
> 
> joerg
> 
Hi Joerg,

What version of Mathematica do you use? I do not get any error message 
withe the following *Plot* command with Mathematica 5.2 for XP:

In[1]:=
Plot[Sin[x], {x, 5.85*^-17, 7.15*^-17}];

In[2]:=
$Version

Out[2]=
"5.2 for Microsoft Windows (June 20, 2005)"

Also, could you post some of your function definitions, that may help to 
understand what is going on.

Best regards,
Jean-Marc


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