Normal Disappear Problem

*To*: mathgroup at smc.vnet.net*Subject*: [mg55302] Normal Disappear Problem*From*: "gouqizi.lvcha at gmail.com" <gouqizi.lvcha at gmail.com>*Date*: Fri, 18 Mar 2005 05:35:18 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hi, All: I have the following parametric equation for an unit sphere: x = cos(u)sin(v) y = sin(u)sin(v) z = cos(v) 0<=u<2*Pi ; 0<=v<=Pi Then I use normal = (Dx/Du, Dy/Du, Dz/Du) CROSS (Dx/Dv, Dy/Dv, Dz/Dv) to get the normal vector. I get the follwoing after calculation (with normalization): normal = [sin(v) ^2 cos(u), sin(v)^2 sin(u), cos(u)^2 cos(v) sin(v) + sin(u)^2 cos(v) sin(v)] Now when u=0, v=0 , Normal = (0,0,0)! How can it be? We know the fact that a sphere should have normal everywhere. Rick

**Follow-Ups**:**Re: Normal Disappear Problem***From:*DrBob <drbob@bigfoot.com>

**Re: Normal Disappear Problem***From:*Daniel Lichtblau <danl@wolfram.com>