//public double GetCorrelation(string factor1, string factor2)

        public override void AddValue(string factor, NArray weights)
        {
            Assertions.AssertIsVectorOfLength(weights, WeightsLength, "weights");
            if (weights.Length != WeightsLength)
            {
                throw new ArgumentException("length mismatch");
            }
            _cache[factor] = weights;
        }