Re: Problem with ->
- To: mathgroup@smc.vnet.net
- Subject: [mg11448] Re: [mg11379] Problem with ->
- From: Bob Hanlon <BobHanlon@aol.com>
- Date: Thu, 12 Mar 1998 01:33:52 -0500
R'[s] does not contain the literal form R[s]
R'[s]
Derivative[1][R][s]
Consequently, you must substitute for both R[s] and R'[s]
subst = R[s] -> k*s;
R[s]/R'[s] /. {subst, D[subst, s]}
s
The approach above readily handles more complicated cases. For example,
subst = R[s] -> k*s^2 Exp[-s];
R[s]/R'[s] /. {subst, D[subst, s]} // Simplify
s/(2 - s)
Bob Hanlon
In a message dated 3/9/98 2:58:34 AM,
hans.steffani@e-technik.tu-chemnitz.de wrote:
>
>I want to substitute R[s] by k s.
>I tried:
>R[s] / R'[s] /. R[s] -> k s
>and got
>k s / R'[s]
>instead of the expected
>s
>
>What am I doing wrong?
>
>Hans Friedrich Steffani