c6e5f6afe0
solver that properly supports constraints with some degrees-of-freedom. The previous solver implementation only used the S matrix (constraint filter matrix) for pinning vertices, in which case all elements are zero and the error doesn't show up. With partial constraints (useful for collision contacts) the matrix has non-zero off-diagonal elements and the algorithm easily diverges. There are also initial steps for implementing collision prevention as described in the Baraff/Witkin paper "Large Steps in Cloth Simulation" (http://www.cs.cmu.edu/~baraff/papers/sig98.pdf).