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Defining derivatives

• To: mathgroup at smc.vnet.net
• Subject: [mg87851] Defining derivatives
• From: dh <dh at metrohm.ch>
• Date: Fri, 18 Apr 2008 07:11:33 -0400 (EDT)

Hello All,

does anybody know how to define symbolic derivatives. E.g.:

f[x_]:=f1[x];

f'[x_]:=f2[x];

this does not work because f on the lefthand side is evaluated. To 

prevent this (do not forget to remove f before redefining it):

f[x_]:=f1[x];

HoldPattern[f'[x_]]:=f2[x];

this gives no message, but f'[x] returns f1[x] instead of f2[x].

The same thinhg happens when you change the sequence of definitions:

f'[x_]:=f2[x];

f[x_]:=f1[x];

Further, where is the information about derivatives stored?

thank's a lot, Daniel

• Follow-Ups:
  • Re: Defining derivatives
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
  • Re: Defining derivatives
    • From: Carl Woll <carlw@wolfram.com>