Calculates accuracy

        :return: Accuracy

def accuracy(self):
        """Calculates accuracy

        :return: Accuracy
        """
        true_pos = self.matrix[0][0]
        false_pos = self.matrix[1][0]
        false_neg = self.matrix[0][1]
        true_neg = self.matrix[1][1]

        num = 1.0 * (true_pos + true_neg)
        den = true_pos + true_neg + false_pos + false_neg

        return divide(num, den)