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Re: message question
*To*: mathgroup at smc.vnet.net
*Subject*: [mg70952] Re: [mg70918] message question
*From*: "Chris Chiasson" <chris at chiasson.name>
*Date*: Thu, 2 Nov 2006 06:48:46 -0500 (EST)
*References*: <200611010856.DAA01601@smc.vnet.net>
in some other posts on MG, I have heard people say that N can be used
to prove two expressions are not equal
my guess is that it only tries to numerically prove the expression is
false if it can't directly prove the expression is true
with the fullsimplify command, some kind of rearrangement must happen
that makes the equality more obvious
On 11/1/06, dimitris <dimmechan at yahoo.com> wrote:
> Consider the following
>
> sols = Solve[x^3 + 2*x^2 - 1 == 0]
> {{x -> -1}, {x -> (1/2)*(-1 - Sqrt[5])}, {x -> (1/2)*(-1 + Sqrt[5])}}
>
> Why do they appear the warning messages in the following command?
>
> x^3 + 2*x^2 - 1 == 0 /. sols
> N::meprec: Internal precision limit $MaxExtraPrecision =
> 49.99999999999999` \
> reached while evaluating \!\(\(-1\) + 1\/2\ \((\(-1\) - \@5)\)\^2 +
> 1\/8\ \(\(\((\(-1\) - \
> \@5)\)\^3\)\(.\)\)\)
> N::meprec: Internal precision limit $MaxExtraPrecision =
> 49.99999999999999` \
> reached while evaluating \!\(\(-1\) + 1\/2\ \((\(-1\) - \@5)\)\^2 +
> 1\/8\ \(\(\((\(-1\) - \
> \@5)\)\^3\)\(.\)\)\)
> {True, -1 + (1/2)*(-1 - Sqrt[5])^2 + (1/8)*(-1 - Sqrt[5])^3 == 0, -1 +
> (1/2)*(-1 + Sqrt[5])^2 + (1/8)*(-1 + Sqrt[5])^3 == 0}
>
> which they don't avoid the verification
>
> FullSimplify[%]
> {True,True,True}
>
> Is it a way to avoid the messages (apart from turn off the message)?
>
> The following seems not to help.
>
> Block[{$MaxExtraPrecision = 1000}, x^3 + 2*x^2 - 1 == 0 /. sols]
>
> Thanks a lot
>
>
--
http://chris.chiasson.name/
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