Nonlinear discriminants

Suppose we have a feature vector v = (v₁ , v₂ , …)^T . A linear discriminant has the form

d = d₀ + d₁ v₁ + d₂ v₂ + …

A nonlinear discriminant can add terms such as w_ijv_iv_j or w_ijjkv_iv_jv_k.

There are more systematic ways of generating nonlinear discriminants, e.g.

http://www.dai.ed.ac.uk/CVonline/LOCAL_COPIES/LI1/kda/