Efficient implementation of minimum deficiency ordering

For fast Cholesky factorization, it is most important to reduce the number of non-zero elements by ordering methods. Generally, minimum deficiency ordering produces less nonzero elements, but it is very slow. We propose a more efficient implementation method. Minimum deficiency ordering requires numerous computations related to adjacent nodes. However, the number of computations is reduced by using indistinguishable nodes, the clique storage structures and the explicit storage structures.