Joint motion map

[Kishor Bhalerao]

Hi Sherm,

What is the easiest way to obtain the H matrix in equation 5.2 described in the
Simbody theory manual ? I am looking only at coarse grained RNA applications
and expect just the regular joint types (free, rigid, revolute, spherical).

The method i used previously was to call the function
matter.getRep().getRigidBodyNode().getDOF() and use a simple switch statement
to generate the required H matrix. However, I also had built all the libraries
from source. I am right now working just with the Simtk2.0 core (its difficult to
build from source and I would like to use some machines in the lab rather than abuse my laptop for longer simulations.). As i understand it, with Simtk2.0 core, i would not have access to the functions declared in RigidBodyNode.h, is that right ? If yes, what are my options ?

Thanks,
Kishor Bhalerao

[Michael Sherman]

Hi, Kishor.

I think you might like this MobilizedBody method:
/// Expert use only: obtain a column of the hinge matrix H corresponding to
/// one of this mobilizer's mobilities.
SpatialVec getHCol(const State& s, UIndex ux) const;

It returns a column of the H matrix; call it once for each mobility of the joint (after you have set q's and realize(Position).

Regards,
Sherm

[Kishor Bhalerao]

Hi Sherm,
I tried using getHCol() and it works out fine for my current purposes.

Thanks,
Kishor.