internal static IList<double> PairwiseAddition(this IList<double> list1, IList<double> list2) { List<double> result = new List<double>(); for (int i = 0; i < list1.Count; i++) { result[i] = list1[i] + list2[i]; } return result; //return list1.Zip(list2, (p, q) => p + q).ToList(); }