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

*To*: mathgroup at smc.vnet.net*Subject*: [mg46305] Re: [mg45482] Problem with FullSimplify in Version 5: Rationals are converted to Reals*From*: oberfeld <oberfeld at uni-mainz.de>*Date*: Fri, 13 Feb 2004 21:57:34 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Dear list, some weeks ago, I posted a question concerning FullSimplify in Ma 5.0 which seems to occur because Rationals are converted to Reals. Thanks to those who suggested work-arounds! Unfortunately, I was not able to resolve my problem following the suggestions. Wolfram support meanwhile confirmed this to be a problem of version 5.0.0 and said that the problem were resolved in Ma 5.0.1. However, after installing the update I had to realize that this is *not correct*. So, for all who are interested, here comes the 'full problem' (and its solution) again: I have to solve a rather nasty expr for a variable deltaL: expr=1/Sqrt[2] == (1/2)*(1 + (1/2)*(-1 - 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])])) + (1/4)*(1 + 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])]); In Ma 3+4, the following straightforward expression works: Solve[FullSimplify[expr],deltaL] In Ma 5, however, the same expression produces the all-too-well-known message "Solve::tdep: The equations appear to involve the variables to be solved for in an essentially non-algebraic way." Switching to Simplify (instead of FullSimplify), as Andrzej & Bob suggested, does not help (at least on my machine). The only solution I found (thank's for the idea, Bob!), was to use Rationalize: N[Solve[Simplify[Rationalize[expr,0]],deltaL]] Out:={deltaL->3.7999} Note, that *FullSimplify* still does not work!! N[Solve[FullSimplify[Rationalize[expr,0]],deltaL]] Would be no problem were it not for many of such expressions lingering in my code, so that I have to step through it and insert that "Rationalize magic" each and every time... ;-( Best wishes Daniel ------------------------------------- Dipl. Psych. Daniel Oberfeld-Twistel University of Mainz Institute of Psychology Experimental Psychology Staudingerweg 9 55099 Mainz Germany T. ++49 (0) 6131 39 22423 Fax. ++49 (0) 6131 39 22480

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