Suppose there are C classes, and the i-th class has Ni
number of training examples. Let Cost[i, c] (i, c ∈ {1..C})
denote the cost of misclassifying an example of the i-th class to
the c-th class (Cost[i, i] = 0), and Cost[i] (i ∈ {1..C}) denote
the cost of the i-th class