Efficient constraint dynamics using MILC SHAKE

We address the problem of imposing rigid constraints between connected sites in a dynamic computer simulation. For two important cases, the linear and ring topologies, each site is connected to at most two nearest neighbors. The constraint matrix is then invertible in order n operations. We show that, this being the case, a computational method based on a matrix inversion of the linearized constraint equations (MILC SHAKE) can be orders of magnitude faster than the simple SHAKE or RATTLE methods.