Is it possible for a matrix to contain a positive match for Y to Y? Where Y could be any DNA letter or protein? Y could be A or B or C... etc etc. Normally, scores range from 0 and up, correct? Are there matrixes in use that can have negative values for an exact identity match? What if a matrix had something like B to B had a score of -1, but W to W had a score of 6. Would such a matrix have any use? I am just asking, because I'm writing some hobbyist bio-informatics software, and... I'm basically learning as I go along, and I'd like to eliminate this possibility if possible, because assuming it's not possible would make it possible for me to write some simpler code. -- http://elfdata.com/plugin/