Re: How do I create a parametric expression?
- To: mathgroup at smc.vnet.net
- Subject: [mg68592] Re: How do I create a parametric expression?
- From: axlq at spamcop.net (axlq)
- Date: Fri, 11 Aug 2006 04:39:58 -0400 (EDT)
- References: <ebc7b6$l58$1@smc.vnet.net> <ebebds$les$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
In article <ebebds$les$1 at smc.vnet.net>, Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com> wrote: > >Use Replace [1] with level specification [2]: Hi Jean-Marc, Thanks for the tip, but I must point out that the example you provided shows that it doesn't work correctly: >expr = -((1 + 2*n)*((a^4*k^2 + a^2*(-1 + k^2*(q - z)^2) + 2*(q - >z)^2)*Cos[k*Sqrt[a^2 + (q - z)^2]] - k*(a^2 - 2*(q - z)^2)*Sqrt[a^2 + (q >- z)^2]*Sin[k*Sqrt[a^2 + (q - z)^2]])*Sin[((1 + >2*n)*Pi*z)/L])/(8*Pi*w*(a^2 + (q - z)^2)^(5/2)) > >Replace[expr, Sqrt[a^2 + (q - z)^2] -> R, {0, Infinity}] > >--> -(((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])/(8*Pi*w*(a^2 + (q - z)^2)^(5/2))) See that last term at the very end: (a^2 + (q - z)^2)^(5/2) This should have been replaced with R^5. Similarly there are other places that could be expressed in terms of R. I don't want a simple substitution; I want a parametric expression in terms of the parameter I define. -Alex