  In this technical report we derive the analytic form of the Hessian matrix
for shape matching energy. Shape matching is a useful technique for meshless
deformation, which can be easily combined with multiple techniques in real-time
dynamics. Nevertheless, it has been rarely applied in scenarios where implicit
integrators are required, and hence strong viscous damping effect, though
popular in simulation systems nowadays, is forbidden for shape matching. The
reason lies in the difficulty to derive the Hessian matrix of the shape
matching energy. Computing the Hessian matrix correctly, and stably, is the key
to more broadly application of shape matching in implicitly-integrated systems.
