Re: High precision numbers and Plot[] ?

• To: mathgroup at smc.vnet.net
• Subject: [mg13702] Re: High precision numbers and Plot[] ?
• From: Paul Abbott <paul at physics.uwa.edu.au>
• Date: Sat, 15 Aug 1998 04:39:30 -0400
• Organization: University of Western Australia
• References: <6qp3b3\$ajn@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```a_kowald wrote:

> I try to plot a function where I have to use high precision numbers.
> That means to get the correct answer I have to use N[f,50]. I set the
> Compiled option of plot to false and tried:
>
> Plot[N[f,50], {i, start, end}, Compiled -> False]
>
> However, this doesn't work. The result is the same as:
> Plot[f,{i,start,end}]
>
> Any idea what I'm doing wrong ?

The likely problem is that the table of values generated by Plot is at
machine precision which overrides the use of N[f,50]. Here is one
workaround by way of an example.  Compare

In[1]:= Plot[LegendreP[50], {x, 0, 1}, PlotRange -> All];

with

In[9]:= Plot[LegendreP[50, SetPrecision[x, 30]], {x, 0, 1},
PlotRange -> All, Compiled -> False];

Cheers,
Paul

____________________________________________________________________
Paul Abbott                                   Phone: +61-8-9380-2734
Department of Physics                           Fax: +61-8-9380-1014
The University of Western Australia            Nedlands WA  6907
mailto:paul at physics.uwa.edu.au  AUSTRALIA
http://www.physics.uwa.edu.au/~paul

God IS a weakly left-handed dice player
____________________________________________________________________

```

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