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MathGroup Archive 2004

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Re: Problem with FullSimplify in Version 5: Rationals are converted to Reals

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45518] Re: Problem with FullSimplify in Version 5: Rationals are converted to Reals
  • From: drbob at bigfoot.com (Bobby R. Treat)
  • Date: Sun, 11 Jan 2004 03:20:20 -0500 (EST)
  • References: <bto17c$2gp$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Version 5.0's is the correct behavior, in my opinion. Either we have
unlimited precision, or we don't. In your expression, we don't--and
the result of FullSimplify is, indeed, simpler after recognizing the
fact.

Bobby

oberfeld <oberfeld at uni-mainz.de> wrote in message news:<bto17c$2gp$1 at smc.vnet.net>...
> Dear list,
> 
> while trying to solve an equation that could be solved without problems 
> in MA 4.2, Solve[] does not find a solution in Ma 5.0.0.0.
> 
> I found that the problem is due to FullSimplify[] in Version 5.
> 
> In Version 4.2,
> Full Simplify[
>      Erf    [
>      (
>      -(Log[10000000000]/Log[10]) -
>      Log[10^(-12 + (20 +deltaL)/10)]/Log[10]
>      )/
>      (Sqrt[2]*Sqrt[0.25302502757884177 +
>      (0.6089140226261116 - 0.005294904544574884*
>          (20 + deltaL))2])
>          ]
>           ]
> 
> yields
> 
> Out:=-Erf[Log[10^(deltaL/10)]/
>      (Sqrt[1.012100110315367 + (-0.010653685371740707 +
>           0.00005607202827231952*deltaL)*deltaL]*Log[10])]
> 
> In Version 5, I get
> 
> Out:=0.5 - 0.25*Erf[(0. - 
> 0.30709257318568767*Log[E^(0.2302585092994046*deltaL)])/
>       Sqrt[0.5060500551576835 + (-0.005326842685870354 + 
> 0.00002803601413615976*deltaL)*
>          deltaL]] +
>    0.25*Erf[(0. + 0.30709257318568767*Log[E^(0.2302585092994046*deltaL)])/
>       Sqrt[0.5060500551576835 + (-0.005326842685870354 + 
> 0.00002803601413615976*deltaL)*
>          deltaL]]
> 
> So, FullSimplify[] in Version 5 has obviously converted *all numbers* to 
> Reals, while in Version 4.2, Rationals are used where available!!
> 
> As a consequence, Solve[] Version 5 can not find a solution to an 
> equation in which the above term appears.
> 
> QUESTION: do you know of a fix available for FullSimplify[] in Version 5 
> that corrects for this behaviour?
> Or are there any Options which can be used to 'reset' FullSimplify[] in 
> Version 5 to the behavior of Version 4.2??
> 
> 
> Best wishes,
> 
> Daniel Oberfeld-Twistel
> 
> ----------------------------
> Daniel Oberfeld-Twistel
> Institute of Psychology
> Experimental Psychology
> University of Mainz
> Staudingerweg 9
> 55099 Mainz
> Germany


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