Re: More on functions & derivatives
- To: mathgroup at smc.vnet.net
- Subject: [mg3526] Re: More on functions & derivatives
- From: Harald Berndt <haraldb at nature.berkeley.edu>
- Date: Wed, 20 Mar 1996 02:51:10 -0500
- Organization: University of California Forest Prodcts Lab
- Sender: owner-wri-mathgroup at wolfram.com
Richard W. Klopp wrote:
>Can someone help me understand what is going
> on?
>
> I define a function:
>
> f[x_] := x^2
>
> I try to plot its first derivative, but get errors instead.
>
> Plot[D[f[x],x],{x,-2,2}]
>
--
Richard:
Jon Guyer gave you the answer for the "why:" D[-1, -1] is not a valid
statement. When dealing with functions involving derivatives, I really
like the way Alfred Gray ("... Differential Calculus ...") makes
explicit use of a dummy variable (we are, after all, doing it, too.
Always! Only implicitly.):
df[x_] := D[f[xx], xx] /. xx -> x
______________________________________________________________________
Harald Berndt, University of California
Research Specialist Forest Products Laboratory
Phone: 510-215-4224 FAX: 510-215-4299
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