Re: Simplifying Derivatives

*To*: mathgroup at smc.vnet.net*Subject*: [mg13163] Re: [mg13051] Simplifying Derivatives*From*: Sean Ross <seanross at worldnet.att.net>*Date*: Mon, 13 Jul 1998 07:42:12 -0400*References*: <199807042044.QAA02843@smc.vnet.net.>*Sender*: owner-wri-mathgroup at wolfram.com

Kenneth S. Crumpton wrote: > > I am computing symbolically derivatives of orbit equations. The answers > are coming out correctly but how do I keep it from substituting what > various symbols are equal to ? (E.g., r = sqrt(x^2+y^2+z^2); I just > want to see r in the answer and not the expansion) Thanks. > > Steve Crumpton > Systems Engineer, Raytheon You will need to use a transformation rule such as expr/.x^2+y^2+z^2->r^2. The use of transformational programming is one of the three programming paradigms in mathematica. If you are going to do anything very complicated(In general, algebraic simplification is complicated), I would recommend a third party book like David Wagners Power Programming book to help you out.

**References**:**Simplifying Derivatives***From:*kcrumpto@redwood.dn.hac.com (Kenneth S. Crumpton)