Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

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/


  • Prev by Date: Re: use a function within a new function
  • Next by Date: Re: use a function within a new function
  • Previous by thread: message question
  • Next by thread: Re: message question