Minimizing storage in implementations of the overlap lattice-Dirac operator

The overlap lattice-Dirac operator contains the sign function epsilon(H). Recent practical implementations replace epsilon(H) by a ratio of polynomials, HPn(H-2)/Q(n)(H-2), and require storage of 2n + 2 large vectors. Here I show that one can use only four large vectors at the cost of executing the core conjugate algorithm twice. The slow-down might be less than by a factor of 2, depending on the architecture of the computer one uses.