Re: How do I create a parametric expression?

*To*: mathgroup at smc.vnet.net*Subject*: [mg68608] Re: How do I create a parametric expression?*From*: axlq at spamcop.net (axlq)*Date*: Fri, 11 Aug 2006 04:40:47 -0400 (EDT)*References*: <200608090819.EAA21141@smc.vnet.net> <ebec2n$lic$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

In article <ebec2n$lic$1 at smc.vnet.net>, gardyloo <gardyloo at mail.wsu.edu> wrote: > I think this question comes up pretty often on the list; it seems to >be one of the harder things to do (or do well, and consistently) with >Mathematica. Usually, it seems that people have to delve into the >FullForm expressions, which can be a huge pain. Yes, from the responses posted to my original query, it seems that there is no straightforward way to do it than by making substitutions one step at a time. Yours is the most efficient suggestion yet, doing most of it in one step: >In[9]:= >expr //. {(a^2 + (q - z)^2)^(n_) -> R^(2*n)} > >Out[9]= > >-((1/(8*Pi*R^5*w))*((1 + 2*n)* > ((a^4*k^2 + a^2*(-1 + k^2*(q - z)^2) + 2*(q - z)^2)* > Cos[k*R] - k*R*(a^2 - 2*(q - z)^2)*Sin[k*R])* > Sin[((1 + 2*n)*Pi*z)/L])) ...and as others have suggested, replacing (q-z)^2 by R^2-a^2 takes it a bit further. -Alex

**References**:**How do I create a parametric expression?***From:*axlq@spamcop.net (axlq)