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