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MathGroup Archive 1999

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Re: Manipulating differential equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18651] Re: Manipulating differential equations
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 15 Jul 1999 01:45:44 -0400
  • Organization: Universitaet Leipzig
  • References: <7m6jti$2mc@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

try

dg1 /. Thread[{#,D[#,x],D[#,x,x]} & /@ (c[x]->Exp[-a x])]

Hope that helps
  Jens

Martin Heimann wrote:
> 
> Dear colleagues,
> 
> I would like to insert test functions into an expression that contains
> differentials:
> 
> dg1 = c''[x] + g c'[x]
> I would like e.g. to replace c[x] by Exp[-a x]:
> 
> dg1/.c[x]->Exp[-a x]
> 
> but this doesn't work; one has to put substitution rules for each of the
> derivatives explicitly. Is there a more elegant way to achieve this?
> 
> Cheers,
> Martin Heimann


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