Re: Simplify[] shortcoming

*To*: mathgroup at smc.vnet.net*Subject*: [mg21554] Re: Simplify[] shortcoming*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Sat, 15 Jan 2000 02:03:59 -0500 (EST)*References*: <85mlo9$1vc@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Gianluca, This doesn't explain the higher leaf count in your results from Simplify and FullSimplify, but: Simplify[Apart[expr]] (3*x)/(x - y) + Log[x] + Log[-1 + y/x] And if you know that x-y is the problem: Collect[expr, x - y] (3*x)/(x - y) + Log[x] + Log[-1 + y/x] Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 "Gianluca Gorni" <gorni at dimi.uniud.it> wrote in message news:85mlo9$1vc at smc.vnet.net... > > Hello! > > I have run into a simple expression for which both Simplify and > FullSimplify cannot see an easy simplification: > > expr = (3*x + (x - y)*Log[x] + (x - y)*Log[-1 + y/x])/(x - y); > > You can see that the factors (x-y) cancel out with the denominator. > So you can write expr as > > (3*x)/(x - y) + Log[x] + Log[-1 + y/x] > > which has a LeafCount of 21, while expr scored 34. Nevertheless, > Simplify[] leaves expr as it was. > > FullSimplify[expr] does collect (x-y) in the numerator, but still > the LeafCount is 29. > > My version is Mathematica 4 on MacOS. > > Gianluca Gorni > >