# 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
Some additional details:
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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