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Re: Manipulating differential equations

• To: mathgroup at smc.vnet.net
• Subject: [mg18576] Re: Manipulating differential equations
• From: "Kevin J. McCann" <kevinmccann at Home.com>
• Date: Tue, 13 Jul 1999 01:01:19 -0400
• Organization: @Home Network
• References: <7m6jti$2mc@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Try this:

f[x_]=Exp[a x];

dg2=dg1/.c->f


Kevin

Martin Heimann <martin.heimann at bgc-jena.mpg.de> wrote in message
news:7m6jti$2mc at smc.vnet.net...
> 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
> ------------------------------------------------------------------
> Max-Planck-Institut fuer Biogeochemie
> Postfach 100164, D-07701 Jena, Germany
> (Street Address: Tatzendpromenade 1a)
>
> Tel.:  +49-3641-64-3773/3701,  Fax.: +49-3641-64-3710
> Email: martin.heimann at bgc-jena.mpg.de
>