trying to "simplify" very large output

*To*: mathgroup at smc.vnet.net*Subject*: [mg83058] trying to "simplify" very large output*From*: "Basjsmit" <basjsmit at wanadoo.nl>*Date*: Fri, 9 Nov 2007 05:11:43 -0500 (EST)

Dear Reader, When I used Mathematica to solve a certain expression, the output was extremely large, somewhere around 10 000 characters. When I looked more closely at the output, I noticed certain frases kept repeating. I havent found anything in the help, but Im wondering if there is a function that can replace those frases with a variable and set that variable once. An example: t-> -(y z-v x Cos[k]^2-v x Sin[k]^2)/(z^2-x^2 Cos[k]^2-x^2 Sin[k]^2)-1/2 \[Sqrt]((4 (y z-v x Cos[k]^2-v x Sin[k]^2) ........ becomes: A = y z-v x Cos[k]^2-v x Sin[k]^2 B = z^2-x^2 Cos[k]^2-x^2 Sin[k]^2 t-> -A / B -1/2 \[Sqrt]((4 A ........ Thanks in advance, Bas PS: just curious, is there a name for the proces I described above?

**Follow-Ups**:**Re: trying to "simplify" very large output***From:*Daniel Lichtblau <danl@wolfram.com>