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From: "John D'Errico" <woodchips@rochester.rr.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Vectors
Date: Wed, 12 Nov 2008 13:28:01 +0000 (UTC)
Organization: John D'Errico (1-3LEW5R)
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"M K" <maha_k@mathworks.com> wrote in message <gfejp2$od9$1@fred.mathworks.com>...
> I have 4 points of a plane, ABCD .Can i calculate the normal vector,n  of it?
> 
> Is it n= cross(AB,CD)?

Are these 4 points that lie in a plane in how many
dimensions?

In 3-d, only 3 points determine a plane. Are all 4
points known to lie in the same plane? (If they are
not coplanar, then you cannot determine a normal
vector.)

So what do you have? Perhaps the simplest solution
to your question is to use null. Assuming that A,B,C,D
are all row vectors, then do this:

N = null([B-A;C-A;D-A]);

John