From: "y Mehta" <mehtayogesh@gmail.(DOT).com>
Newsgroups: comp.soft-sys.matlab
Subject: Angle between two vectors
Message-ID: <ef5ce9c.-1@webcrossing.raydaftYaTP>
Date: Mon, 9 Jul 2007 17:16:29 -0400
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Xref: comp.soft-sys.matlab:418088

How do I find the angle between two unit vectors a and b? I know I
can find cosine theta by the following formula:

theta = acos(dot(a,b));

However, how do I know whether the angle is actually theta, or -theta
or pi-theta or pi+theta??

Notice that the vectors are in three dimension (3d).