these are good: http://math.lanl.gov/~brendt/Publications/wohlberg-1999-review.shtml http://math.lanl.gov/~brendt/Publications/wohlberg-1999-revi... http://www.

these are good: http://math.lanl.gov/~brendt/Publications/wohlberg-1999-review.shtml http://math.lanl.gov/~brendt/Publications/wohlberg-1999-revi... http://www.faqs.org/faqs/compression-faq/part2/section-8.html http://www.faqs.org/faqs/compression-faq/part2/section-8.htm...