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MathGroup Archive 2003

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Re: Re: This should evaluate to zero

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39999] Re: [mg39956] Re: [mg39926] This should evaluate to zero
  • From: Dr Bob <drbob at bigfoot.com>
  • Date: Fri, 14 Mar 2003 04:46:00 -0500 (EST)
  • References: <200303130802.DAA11952@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

Replacing the "exact" computation with an approximate one doesn't show that 
the original expression is zero.  It only shows it is zero to machine 
precision.

Bobby

On Thu, 13 Mar 2003 03:02:09 -0500 (EST), Y.A.Tesiram 
<yas at pcomm.hfi.unimelb.edu.au> wrote:

> Hi,
> As you have written it, your expression is exact. Forcing a numerical
> approximation of the expression with
>
> N[ArcSinh[1]-Log[3363+2378*Sqrt[2]]/10]
>
> gives
>
> 0.
>
> -- a very very small number which for all purpose and sense is zero.
> Rather than use integers in your expression you can use reals by writing
> the decimal point. Mathematica will retrun a very very small number
> depending on the setting of the variable $MaxExtraPrecision and the very
> small number can be carried through in subsequent calculations. Some
> degree of care must be taken in deciding what level of numerical 
> precision
> is needed and the actual problem at hand.
>
> Yas
>
>
> On Wed, 12 Mar 2003, jf alcover wrote:
>
>> Bonjour,
>> Methinks that the following expression should evaluate to zero,
>> but it does not, even with
> FullSimplify :
>> ArcSinh[1]-Log[3363+2378*Sqrt[2]]/10
>> Could anyone explain ?
>>
>>
>
>
>



-- 
majort at cox-internet.com
Bobby R. Treat



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