  We present a variation on classic beam thresholding techniques that is up to
an order of magnitude faster than the traditional method, at the same
performance level. We also present a new thresholding technique, global
thresholding, which, combined with the new beam thresholding, gives an
additional factor of two improvement, and a novel technique, multiple pass
parsing, that can be combined with the others to yield yet another 50%
improvement. We use a new search algorithm to simultaneously optimize the
thresholding parameters of the various algorithms.
