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MathGroup Archive 1995

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Re: Oh why is life never easy? Need help with |vector|

  • Subject: [mg2800] Re: [mg2771] Oh why is life never easy? Need help with |vector|
  • From: mathes at esaab.math.missouri.edu (Elias Saab)
  • Date: Mon, 18 Dec 1995 00:42:09 -0500
  • Approved: usenet@wri.com
  • Distribution: local
  • Newsgroups: wri.mathgroup
  • Organization: Wolfram Research, Inc.


 Your original code had {} around the answer. Take 
them out and your problem will be solved.
Of course Mma will consider what you  have
{a = Sqrt[(u[[1]]^2+u[[2]]^2+u[[3]]^2)]}
as a vector.
Try this code:

 absvec[u_] :=
                Module[{a},
                a = Sqrt[(u[[1]]^2+u[[2]]^2+u[[3]]^2)]]

In fact one can define |v| as Sqrt[ v . v]

Elias Saab

On Sat, 16 Dec 1995, ULI WORTMANN wrote:

> Hi All,
> 
> I need to calculate v0 = v / |v| where v is a vector of size 3.
> However, |v|, which is a scalar, is for some reason (I don't
> understand) treated like a vector (at least VectorQ[|v|] gives
> TRUE). Obviously, it is impossible to divide two vectors of different
> length. 
> 
>  |v| is defined as:
> 	absvec[u_] :=
> 		Module[{a},
> 		{a = Sqrt[(u[[1]]^2+u[[2]]^2+u[[3]]^2)]}]
> 
> and called as u = 1/absvec[v]
> 
> To bad I have no idea what's wrong with this code. Any input is
> appreciated.
> 
> 	ThanX
> 		Uli
> -- 
> 	Uli Wortmann
> 
> 	Dept. of Geology       Fax (Germany) 89 3209 3168
> 	Tech. Univ. Munich     Fon		     3232
> 	email: uli at homer.geol.chemie.tu-muenchen.de
> 


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