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Re: Defining derivatives

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87868] Re: [mg87851] Defining derivatives
  • From: Carl Woll <carlw at wolfram.com>
  • Date: Sat, 19 Apr 2008 03:32:41 -0400 (EDT)
  • References: <200804181111.HAA18885@smc.vnet.net>

dh wrote:

>Hello All,
>
>does anybody know how to define symbolic derivatives. E.g.:
>
>f[x_]:=f1[x];
>
>f'[x_]:=f2[x];
>  
>
Use

Derivative[1][f] = f2

Carl Woll
Wolfram Research

>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
>
>
>  
>



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