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

*To*: mathgroup at smc.vnet.net*Subject*: [mg46306] Re: [mg45482] Problem with FullSimplify in Version 5: Rationals are converted to Reals*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Fri, 13 Feb 2004 21:57:36 -0500 (EST)*References*: <402D01EB.6040505@uni-mainz.de>*Sender*: owner-wri-mathgroup at wolfram.com

For all its worth here is another way that uses Hold instead of Rationalize: Solve[ReleaseHold[Simplify[(If[NumericQ[#] && Head[#] =!= Real, Hold[#], #] & ) //@ expr]], deltaL] Inverse functions are being used by Solve so some solutions may not be found; use Reduce for complete solution information. {{deltaL -> 3.7998970410976023, Erf[(0.3070925731856876*(2.302585092994046*(0.1*deltaL - 10.) + 23.025850929940457))/ Sqrt[(0.6089140226261116 - 0.005294904544574884*(deltaL + 20.))^2 + 0.25302502757884177]] -> 0.41421356237309503}} The "two rule" form of the solution is curious and surprised me, but we can check that the solution is self-consistent: %[[1,2]]/.%[[1,1]] 0.414214->0.414214 On 13 Feb 2004, at 17:57, oberfeld wrote: > 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 > > > > Andrzej Kozlowski Chiba, Japan http://www.mimuw.edu.pl/~akoz/