The slack variable ξ n associated with data vector φ(G n ) allows, if it is nonzero, violation of the constraint y n (w •φ(G n )+b) ≥ 1 that it lies (i) on the correct side of the decision boundary and (ii) outside of or on the boundary of the margin. The first term in the objective function describes the size of the margin; the second term penalizes constraint violations. The hyperparameter C ≥ 0 trades a large margin for constraint violations.