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Re: needed.

• To: mathgroup at smc.vnet.net
• Subject: [mg127065] Re: needed.
• From: awnl <awnl at gmx-topmail.de>
• Date: Thu, 28 Jun 2012 04:00:18 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <23314523.14289.1340701923445.JavaMail.root@m06> <jsefcl$i9u$1@smc.vnet.net>

Hi,

> Plot[Exp[8*(10 - Abs[10 - 20000*x])]*(1 -
>      Erf[(8*(10 - Abs[10 - 20000*x]))^(1/2)]), {x, 0, 1*10^(-3)},
>   PlotRange ->  Full,
>   WorkingPrecision ->  6]
>
> And then maybe someone can explain why MachinePrecision fails but a
> WorkingPrecision as low as 6 works.

I think that's because Mathematica will use "arbitrary precision 
numbers" (software emulated) instead of "machine precision numbers" 
whenever WorkingPrecision is set to something different than 
MachinePrecision, most probably using completely different algorithms 
for anything related to tracking precision.

It's probably even more surprising if you compare 
WorkingPrecision->MachinePrecision with WorkingPrecision->$MachinePrecision

hth,

albert