According to Vapnik’s formulation (Vapnick, 1999), in oneagainstall support vector machines, an n class problem is converted
into n two-class problems and for the ith two-class problems,
class i is separated from the remaining classes. But by
these formulation unclassifiable regions exists, if we use the discrete
decision function. We can resolve unclassifiable regions by
determining the decision functions all-at-once (Vapnick, 1999).