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MathGroup Archive 1998

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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.


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