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Re: Re: defining a function with D

• To: mathgroup at smc.vnet.net
• Subject: [mg37189] Re: [mg37170] Re: defining a function with D
• From: Andrzej Kozlowski <andrzej at platon.c.u-tokyo.ac.jp>
• Date: Wed, 16 Oct 2002 14:25:12 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

(Somehow the original posting never reached me). But what's wrong with

dfx[x_, t_] := Derivative[1, 0][f][x, t]
?

Regards

Andrzej


Yokohama, Japan
http://www.mimuw.edu.pl/~akoz/
http://platon.c.u-tokyo.ac.jp/andrzej/


On Tuesday, October 15, 2002, at 05:17 PM, Jens-Peer Kuska wrote:

> Hi,
>
> f[x_, t_] := Sin[x*t]
> dfx[x_, t_] := Module[{y, df},
>                  df = D[f[y, t], y];
>                  Block[{y = x},
>                    df
>                   ]
>                 ]
>
> Regards
>   Jens
>
> Jason Miller wrote:
>>
>> Dear Listers,
>>
>> I find myself defining functions in terms of differentiation.  For 
>> example,
>>
>> f[x_,t_]:=Sin[x*t]
>> dfx[x_,t]:=D[Sin[y,t],y]/.y->x
>>
>> This works well, but it seems to me that there should be a better way
>> to do this.  That is, there should be a better way to define a
>> 'derivative' of a previous function without going through the
>> replacement contortions.   I can't find the answer in the archive.
>> Can someone tell me the most straightforward way to do this?  Will it
>> work to define a gradient vector or Jacobian matrix?  A Hessian
>> matrix?
>>
>> Thanks in advance.
>> --
>> Jason Miller, Ph.D.
>> Division of Mathematics and Computer Science
>> Truman State University
>> 100 East Normal St.
>> Kirksville, MO  63501
>> http://vh216801.truman.edu
>> 660.785.7430
>
>
>