Re: how do you prevent numerator expansion when using 'Together'?

*To*: mathgroup at smc.vnet.net*Subject*: [mg122316] Re: how do you prevent numerator expansion when using 'Together'?*From*: Alexei Boulbitch <Alexei.Boulbitch at iee.lu>*Date*: Tue, 25 Oct 2011 06:15:55 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Hi, You also can try the following. Assume that you have your complex expression instead of this expr = 1/(d*g)*(a*g + b*g + a*e + b*e + a*f + b*f) (a e + b e + a f + b f + a g + b g)/(d g) simple one. The third part of it is the numerator: expr[[3]] a e + b e + a f + b f + a g + b g This can be also seen by the TreeForm. Then let us factor it: MapAt[Factor, expr, {3}] ((a + b) (e + f + g))/(d g) I hope this helps. Best, Alexei DrMajorBob wrote: > Factor[(a + b)/d + ((a + b)*(e + f))/(d*g)] > > ((a + b) (e + f + g))/(d g) > > Together[(a + b)/d + ((a + b)*(e + f))/(d*g)] > > ((a + b) (e + f + g))/(d g) > > Yes, this simplified example does this on my system too, but the actual expression I have behaves the way I described. Your counter-example indicates there must be something in my actual expression that causes the behavior. I'll experiment to see what that might be. Thanks for pointing this out. - Dushan > On Sat, 22 Oct 2011 05:07:37 -0500, Dushan Mitrovich <dushanm at nnips.net> > wrote: > >> I'm using Mathematica 8. When using 'Together' on an expression the >> numerator >> is always expanded, complicating the appearance of the final result: >> >> In: Together[ (a+b)/d + ((a+b)*(e+f))/(d*g) ] >> Out: 1/(d*g) * (a*g + b*g + a*e + b*e + a*f + b*f) >> >> Instead, I'd much prefer the simpler form >> 1/(d*g) * (a+b)*(g+e+f) >> >> What do I need to do to get the latter form? Thanks. >> >> - Dushan >> [ reverse the middle word of address to reply ] >> > > Alexei BOULBITCH, Dr., habil. IEE S.A. ZAE Weiergewan, 11, rue Edmond Reuter, L-5326 Contern, LUXEMBOURG Office phone : +352-2454-2566 Office fax: +352-2454-3566 mobile phone: +49 151 52 40 66 44