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MathGroup Archive 1998

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Re: Derivatives D[ ] as Functions inside Tables; Need Help!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13193] Re: [mg13102] Derivatives D[ ] as Functions inside Tables; Need Help!
  • From: "Jrgen Tischer" <jtischer at col2.telecom.com.co>
  • Date: Mon, 13 Jul 1998 07:42:42 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Anthony,

I recommend you read first

2.4.8 Immediate and Delayed Definitions

in the Book. Then you will understand that you tried to calculate things
like

D[a Cos[0] + a^2 Sin[0],0]

(so the message General::ivar: 0 is not a valid variable).

Jrgen

-----Original Message-----
From: AES <siegman at ee.stanford.edu>
To: mathgroup at smc.vnet.net
Subject: [mg13193] [mg13102] Derivatives D[ ] as Functions inside Tables; Need
Help= !


>I'm trying to define a function f1[a,x] and its derivative f2[a,x],
>where from my point of view x is the independent variable and   "a" is
>a parameter I'll change on different runs.  So I write, as a simple
>example:
>
>   Remove["Global`*"]
>
>   f1[a_,x_] :=a Cos[x] + a^2 Sin[x]
>
>   f1[a,x]
>
>   f2[a_,x_] := D[f1[a,x],x]
>
>   f2[a,x]
>
>   a=2
>
>   f1[a,x]
>
>   f2[a,x]
>
>   Table[{x, f1[a,x], f2[a.x]} // N, {x,0,4}] // TableForm
>
>and everything looks fine -- except the function f2[a,x] will not
>evaluate inside the Table[ ].  I don't understand this -- help in
>understanding will be much appreciated.
>
>     siegman at ee.stanford.edu
>



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