A monotonic matrix of order n is an n × N matrix in which every element is either 0 or contains a number from the set {1, 2, ..., n} subject to 3 conditions:
the filledin entries in each row are strictly increasing;
the filledin entries in each column are strictly decreasing;
for two filledin cells with same entry, the one further right is higher (the positive slope condition).
See A070214 for more information.
