thanks! What I want is a similar thing to AngleTripletScore, but for a distance metric over rotation tensor between two reference frames. Computing the distance per se is not the hard part (this could be in Euler angles or between the quaternion or a geodesic on the unit sphere) - the painful part is computing the derivative in Cartesian coordinates form. I was hoping somebody went through this pain already... :)

On Tue, Mar 25, 2014 at 6:55 PM, Ben Webb ben@salilab.org wrote:

> On 3/25/14, 6:47 PM, Barak Raveh wrote: > >> Does anybody know of an existing implementation of a harmonic restraint >> on rotational degrees of freedom? >> > > Sure, this is essentially how an angle restraint works in the CHARMM > forcefield, for example. > > > Namely, I have two reference frame of two particles p1 and p2. For >> simplicity, assume xyz(p1) = xyz(p2). I would like to add a harmonic >> restraint over the delta in their reference frame, for some definition >> of that delta. >> > > You just need to encode that delta (e.g. as a PairScore) then plug it into > the existing framework. For example, see core::AngleTripletScore. > > Ben > -- > ben@salilab.org http://salilab.org/~ben/ > "It is a capital mistake to theorize before one has data." > - Sir Arthur Conan Doyle >