Subject: Ambiguous rotation values

From: Boris Gorelik <bgbg:at:pob.huji.ac.il>
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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