Simplifying complicated expressions

*To*: mathgroup at smc.vnet.net*Subject*: [mg110161] Simplifying complicated expressions*From*: "S. B. Gray" <stevebg at ROADRUNNER.COM>*Date*: Sat, 5 Jun 2010 07:31:08 -0400 (EDT)*Reply-to*: stevebg at ROADRUNNER.COM

Suppose I have a long complex expression in which terms like (x^2+y^3-x^2y^2+Sqrt[z3+y2]) (for a simple example) appear many times along with various powers and the reciprocals of it, etc. To make the expression comprehensible and to make the computation faster, I would like to substitute say "f1xyz" for it everywhere it appears. The normal /. and -> substitutions and patterns are not adequate for this. Of course at evaluation time I want to compute f1xyz only once and not have the final formula revert to the original variables. How do I prevent that? Also a welcome addition to Mathematica would be the ability to find these repeated expressions automatically and put them in, because doing it manually is very error-prone and slow. Tips will be appreciated! Steve Gray