Re: Ask Mathematica to sub for a long expression

*To*: mathgroup at smc.vnet.net*Subject*: [mg71933] Re: Ask Mathematica to sub for a long expression*From*: "dimitris" <dimmechan at yahoo.com>*Date*: Mon, 4 Dec 2006 06:39:23 -0500 (EST)*References*: <ekp4o4$2fq$1@smc.vnet.net><ekudat$86k$1@smc.vnet.net>

-a - b /. (n_.)*a + (m_.)*b -> c c 2*a + 2*b /. (n_.)*a + (m_.)*b -> c c Look at the FullForm of expressions FullForm[-a - b] Plus[Times[-1,a],Times[-1,b]] FullForm[2a+2b] Plus[Times[2,a],Times[2,b]] Information["_.", LongForm -> False] p:v is a pattern object which represents an expression of the form p, which, \ if omitted, should be replaced by v. Regards Dimitris aaronfude at gmail.com wrote: > Hi, > > Thanks for all the responses. It doesn't quite work for me, but maybe > with a little extra expertise it will. The problem is that that pattern > is not always obvious w/o extra algebra. The basic problem is > summarized in the fact that the following doesn't work the way I'd like > it to: > > -a-b/.a+b->c > > 2a+2b/.a+b->c > > Many thanks in advance! > > Aaron Fude