Re: Cross results?

*To*: mathgroup at smc.vnet.net*Subject*: [mg63206] Re: [mg63201] Cross results?*From*: "David Park" <djmp at earthlink.net>*Date*: Mon, 19 Dec 2005 07:00:59 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Virgil, Because Mathematica is doing approximate number arithmatic it isn't certain that the result is exactly zero - although in this case it is. Either use Chop or exact calculations. Cross[{10 Sin[x], -10 Cos[x], 2.5}, {0.12 Sin[x], -0.12 Cos[x], 0.0}] // Chop {0.3 Cos[x], 0.3 Sin[x], 0} Cross[{10 Sin[x], -10 Cos[x], 5/2}, {12/100 Sin[x], -12/100 Cos[x], 0}] {(3*Cos[x])/10, (3*Sin[x])/10, 0} David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Virgil Stokes [mailto:virgil.stokes at it.uu.se] To: mathgroup at smc.vnet.net I have the following x=. Cross[{10 Sin[x],-10 Cos[x],2.5},{0.12 Sin[x],-0.12 Cos[x], 0.0}] which gives, {0.3 Cos[x], 0.3 Sin[x], 0.Cos[x]Sin[x]} why does it not set the last term to 0.0?