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MathGroup Archive 2004

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Re: Simplify, Condition, Assuming and SetDelayd

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52370] Re: Simplify, Condition, Assuming and SetDelayd
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Thu, 25 Nov 2004 05:49:40 -0500 (EST)
  • Organization: The University of Western Australia
  • References: <co1e8d$sf0$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <co1e8d$sf0$1 at smc.vnet.net>,
 alvaro diaz <alvarodiazfalconi at yahoo.com> wrote:

> I'm write my Norm function with 
> 
> ... (etc)
> DoubleBracketingBar[ z_ ] := Abs[z] /; Element[ z,
> Complexes ]; 
> DoubleBracketingBar[ v_ ] := Sqrt[v . Conjugate[v]] /;
> Element[ v, Vectors ]; 

There is no Vectors domain in Mathematica. To add a domain see The 
Mathematica Journal 7(4): 450-451.

Why not just use Norm? It automatically handles these two cases. If you 
like you can write
  
 DoubleBracketingBar := Norm

> Then, i'm try to evaluate
> 
> FullSimplify[DoubleBracketingBar[ z_ ]  == Abs[z], z
> ?¸ Complexes]
> 
> but do not work. (This is, the answer is not True)

Because the Condition is held. Try

 Trace[FullSimplify[DoubleBracketingBar[z] == Abs[z],
   Element[z , Complexes]]

to see why.

Cheers,
Paul

-- 
Paul Abbott                                   Phone: +61 8 6488 2734
School of Physics, M013                         Fax: +61 8 6488 1014
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Crawley WA 6009                      mailto:paul at physics.uwa.edu.au 
AUSTRALIA                            http://physics.uwa.edu.au/~paul


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