Nodes
Key Nodes in Intervaled Real Fn refers to the nodes d₁, d₂ , ... , dᵣ₋₁ as described in Intervaled Real Fn
It must be an array of dates with r - 1 elements, whereby r can be any positive integer that represents the number of consecutive time intervals defined by the dates here.
If this array is empty, i.e. if r = 1, then there exists only one time interval that equals the whole time axis and the Intervaled Real Fn becomes identical with ƒ₁, of which the domain equals the whole time axis.