Re: vector representation

*To*: mathgroup at smc.vnet.net*Subject*: [mg82791] Re: vector representation*From*: David Bailey <dave at Remove_Thisdbailey.co.uk>*Date*: Wed, 31 Oct 2007 06:09:06 -0500 (EST)*References*: <fg6r8c$e19$1@smc.vnet.net>

Vlad Luca wrote: > Hi, > Having the vector r(a,b,c) = {a i, b j, c k} where i, j, k are the unit vectors and a, b, c arbitrary coefficients, I want to calculate, for example r(1,2,1) etc. Also I want to be able to add 2 or more of such vectors trough their indexes, for example: r(0,0,1) + r(1,2,3) and the sum to be expressed like this r(1,2,4) and not like {1i, 2j, 4k}. > Thank You in advance! > Mathematica lets you define your own notation, so you could manipulate vectors represented as r[a,b,c] (note that you must use square brackets here): r /: r[a1_, b1_, c1_] + r[a2_, b2_, c2_] := r[a1 + a2, b1 + b2, c1 + c2] r[1, 2, 3] + r[3, 4, 5] (out) r[4, 6, 8] However, I would use the standard notation for now until you get used to Mathematica. The standard notation for a vector is a list. David Bailey http://www.dbaileyconsultancy.co.uk