Defining a derivative that distributes for a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg64222] Defining a derivative that distributes for a function*From*: Andres Corrada-Emmanuel <acorrada at physics.umass.edu>*Date*: Tue, 7 Feb 2006 03:35:48 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hello, I'm trying to define a derivative for a function that distributes: D[f[expr_],x_] ^:= f[D[expr,x]] This gives me: D[f[x^2],x] = f[2x] and D[f[x^4],x] = f[4x^3] But D[f[x^2] + f[x^4],x] = 2xf'[x^2] + 4x^3f'[x^4] instead of the desired: D[f[x^2] + f[x^4],x] = f[2x] + f[4x^3]. Why? And how do I get the desired behaviour. -------------------------------------- Andres Corrada-Emmanuel Lecturer in Physics Physics Department University of Massachusetts at Amherst --------------------------------------

**Follow-Ups**:**Re: Defining a derivative that distributes for a function***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>