[wjordan]

Are you pulling the list of teams at the event for the event from a separate request (i.e. not deriving it from from parsed match data)? If so, you may have to go through your list of teams and eliminate no-shows, because they will appear on the TBA (assuming you are using TBA data) teams list, but not in any matches, causing the row/column for that no-show team in the original match matrix to be all zeroes, making Ax = b underdetermined and thereby unsolvable. This would also lead to your problem of A'A being a singular matrix, and therefore not strictly diagonally dominant.