// sum(w_kj sum( d_i w_ij, i ), j) = sum(w_kj c_j, j)
//
// where again, we remember where the sums over j are over at most two elements,
-// since w_ij is nonzero for at most two values of j.
+// since w_kj is nonzero for at most two values of j.
template<class T>
void optimize_sum_sq_error(const Tap<float>* weights, unsigned num_weights,
Tap<T>* bilinear_weights, unsigned num_bilinear_weights,