Re: Vectors,Norms and assumptions

*To*: mathgroup at smc.vnet.net*Subject*: [mg82789] Re: Vectors,Norms and assumptions*From*: Szabolcs Horvát <szhorvat at gmail.com>*Date*: Wed, 31 Oct 2007 06:08:04 -0500 (EST)*References*: <fg6rjo$e89$1@smc.vnet.net> <fg722g$jsf$1@smc.vnet.net>

Peter Breitfeld wrote: > 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] Or, for as long as you (the OP) are working only with vectors, you could define your own rnorm function as rnorm = Sqrt[#.#]& -- Szabolcs