Correlation.cs: Changed to IEnumerable implementation and some efficiency improvements.
Correlation.cs: Changed to IEnumerable implementation and some efficiency improvements.

shaia/mathnet-numerics,mathnet/mathnet-numerics,shaia/mathnet-numerics,shaia/mathnet-numerics,mathnet/mathnet-numerics,shaia/mathnet-numerics,mathnet/mathnet-numerics,mathnet/mathnet-numerics,mathnet/mathnet-numerics,shaia/mathnet-numerics