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Re: Vectors,Norms and assumptions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg82766] Re: Vectors,Norms and assumptions
  • From: Peter Breitfeld <phbrf at t-online.de>
  • Date: Tue, 30 Oct 2007 05:44:41 -0500 (EST)
  • References: <fg6rjo$e89$1@smc.vnet.net>

sapsi schrieb:
> Hello,
> 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?
>
> 2. On a similar note, i have
> n={an1,an2}
> a={aa1,aa2}
> (*an1,an2,aa1,aa2 are all reals*)
> x=Norm[y(n-a)]
>>> Sqrt[Abs[(-aa1 + an1) y]^2 + Abs[(-aa2 + an2) y]^2]
>
> Once again, how do i indicate that y ,an1,an2,aa1,aa2 are reals?
>
> Thank you for your time and help.
> Rgds
> Bveo
>
>

You could write a function

RNorm[x_]:=Simplify[Norm[x]//.Abs[u]^2:>u^2]

I use this function frequently and it seems to work ok.

Gruss Peter
-- 
==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de


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