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Re: Vectors,Norms and assumptions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg82786] Re: Vectors,Norms and assumptions
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Wed, 31 Oct 2007 06:06:30 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fg6rjo$e89$1@smc.vnet.net>

sapsi wrote:

> I have a question in mathematica (actually 3).
> 
> 1. Let v be v={av1,av2} , then Norm[v]=Sqrt[Abs[av1]^2 + Abs[av2]^2]
> Q: How do indicate to mathematica that av1 and av2 belong to reals?

<snip>

You could use *Simplify* with the *Assumptions* option as in the 
following example.

In[1]:= v = {av1, av2};
Norm@v
Norm@v // Simplify[#, Assumptions -> Element[v, Reals]] &

Out[2]= Sqrt[Abs[av1]^2 + Abs[av2]^2]

Out[3]= Sqrt[av1^2 + av2^2]

Regards,
-- 
Jean-Marc


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