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