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

*To*: mathgroup at smc.vnet.net*Subject*: [mg122352] Re: how do you prevent numerator expansion when using 'Together'?*From*: Dushan Mitrovich <dushanm at nnips.net>*Date*: Wed, 26 Oct 2011 17:38:25 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <j862a7$5l5$1@smc.vnet.net>

Alexei Boulbitch wrote: > 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. Thanks, Alexei. I'd never used 'MapAt' before, so this new tool (for me) is really helpful. - Dushan [ reverse middle word of address to reply ] > > 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 > >