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MathGroup Archive 2003

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Re: Problems evaluating Grad

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39393] Re: Problems evaluating Grad
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 14 Feb 2003 03:17:34 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <b2fpvg$k66$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

the answer of
In[]:= <<Calculus`VectorAnalysis`
In[]:= f[x_,y_]:=x+y;
       Grad[f[a,b]]

is

Out[]={0,0,0}

because a, and b don't depend on x,y,z

If Mathematica does not find a rule, that apply to
an expression it leave the expression unchanged
and if nothing happen you have rpbably not loaded
the Calculus`VectorAnalysis` package.

Regards
  Jens



Konrad Den Ende wrote:
> 
> I'd like to detrmine Grad to a function so i go:
> <<Calculus`VectorAnalysis`
> f[x_,y_]:=x+y
> 
> Grad[f[a,b]]
> 
> I get no errors, but the answer is simply the same thing
> that i asked, as if no computation was done. What do i
> do wrong?
> 
> Also - when i evaluated the examples in Help i got the same
> behavior. The answer that already is there gets exchanged
> to something else upon my evaluation. Namely, the question
> itself. What is that?!
> 
> --
> 
> Vänligen
> Konrad
> ---------------------------------------------------
> phone #1:  (+46/0) 708 - 70 73 92
> phone #2: (+46/0) 704 - 79 96 95
> url: http://konrads.webbsida.com
> e-mail: chamsterkonrad at bigfoot.com
> -----------------------------------
> 
> Sleep - thing used by ineffective people
>             as a substitute for coffee
> 
> Ambition - a poor excuse for not having
>                  enough sence to be lazy
> ---------------------------------------------------


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