# Ambiguous rotation values

• From: Boris Gorelik <bgbg:at:pob.huji.ac.il>
• Subject: Ambiguous rotation values
• Date: Sun, 29 Jun 2003 18:38:14 +0000

```Dear All,
We are trying to sample all possible rotations of a rigid ligand in a discrete
3D space. We define the rotation using a1x, a2x, a3x and A, where
(a1x,a2x,a3x) is the unit vector in the direction of the axis and A is the
angle of rotation in radians. The unit vector is defined by two degrees of
freedom namely: spherical angles theta and phi, and is calculated from them.
We are using the rotate function from the BTL package
(http://bioinformatics.org/project/?group_id=184)
Unfortunately, sometimes we get identical conformations, while using different
input to the function. How can this problem can be avoided?
Every idea will be highly appreciated
PS
we use discrete value for phi, theta and A:
0<phi<2*PI,
0<A<2*PI,
0<theta<PI
a1x=sin(theta)*cos(phi),
a2x=sin(theta)*sin(phi),
a3x=cos(theta).
The rotate function is based on the following rotation matrix:
[cosA+a1x.a1x(1-cosA)      -a3xsinA+a1a2(1-cosA)	a2xsinA+a1xa3x(1-cosA) ]
[a3xsinA+a1xa2(1-cosA)    cosA+a2xa2x(1-cosA)   	-a1xsinA+a2xa3x(1-cosA)]
[-a2xsinA+a3xa1x(1-cosA)   a1xsinA+(1-cosA)a2xa3x 	cosA+(1-cosA)a3xa3x   ]
--
Boris Gorelik
-= ( 2*b || !(2*b)) That's the question =-
Sun, 29/Jun/2003, 30 Sivan 5763
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