Re: Algebraic Manipulation

*To*: mathgroup at smc.vnet.net*Subject*: [mg46188] Re: [mg46159] Algebraic Manipulation*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Tue, 10 Feb 2004 00:06:01 -0500 (EST)*References*: <200402091054.FAA20968@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 9 Feb 2004, at 11:54, David Park wrote: > Dear MathGroup, > > I'm always interested in Mathematica techniques for manipulating and > simplifying algebraic expressions. I came across the following > problem, which I was only able to do with a fair amount of difficulty. > > expr = x*y*(-(z^2/(r^2*(x^2 + y^2))) - 1/(r*(k + r)) + 1/(x^2 + y^2)) > > where > > r^2 == x^2 + y^2 + z^2 > > reduces to > > (k*x*y)/(r^2*(k + r)) > > I wonder if anyone can show an elegant or short method to do the > simplification? > > (The problem arose in calculating the components of the Schwarzschild > metric in Cartesian coordinates.) > David, Simplify[expr, r^2 == x^2 + y^2 + z^2] (k*x*y)/(r^2*(k + r)) I suspect you did not try this because it was too obvious ;-) Andrzej Andrzej Kozlowski Chiba, Japan http://www.mimuw.edu.pl/~akoz/

**References**:**Algebraic Manipulation***From:*"David Park" <djmp@earthlink.net>