Step1) How to select the pairs
Criterion 1: maximize the instantaneous expected maximum likelihood ratio - takes exponential time in X to compute
Criterion 2: randomly select from inferred border points - takes O(X) time to compute
Criterion 3: randomly select from X - takes O(X) time to compute
Criterion 4: maximize E0(x) + E1(x), where Ez(x) = number of errors when f(x) is assigned to z - takes O(X2) time to compute