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MathGroup Archive 2004

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45482] Problem with FullSimplify in Version 5: Rationals are converted to Reals
  • From: oberfeld <oberfeld at uni-mainz.de>
  • Date: Sat, 10 Jan 2004 00:00:30 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

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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