On Mon, Jan 9, 2012 at 3:20 PM, Geoffrey Irving <irving at naml.us> wrote: > Ah, right. ?I'm using incomplete Cholesky as a preconditioner, which > usually won't be stable on the subspace. ?The subspace is derived from > freezing the normal velocity of points involved in collisions, so it > has no useful algebraic properties. > > It's not too difficult to symbolically apply P to A (it won't change > the sparsity), but unfortunately that would make the sparsity pattern > change each iteration, which would significantly increase the cost of > ICC.
Sorry, that sentence was poorly phrased. I meant that it's not too difficult to symbolically eliminate the relevant subspace from A, but that this would produce a matrix whose size changes each time around. I could also replace A with PAP directly without changing the sparsity pattern, but I imagine incomplete Cholesky might choke on the result, which would be a 3x3 block matrix with a lot of singular diagonal blocks. Geoffrey
