Compression algorithm for multi-determinant wave functions

A compression algorithm is introduced for multi-determinant wave functions which can greatly reduce the number of determinants that need to be evaluated in quantum Monte Carlo calculations. We have devised an algorithm with three levels of compression, the least costly of which yields excellent results in polynomial time. We demonstrate the usefulness of the compression algorithm for evaluating multi-determinant wave functions in quantum Monte Carlo calculations, whose computational cost is reduced by factors of between 1.885(3) and 25.23(4) for the examples studied. We have found evidence of sub-linear scaling of quantum Monte Carlo calculations with the number of determinants when the compression algorithm is used.