ch-ch-update: series, closed-form series, and strides

[Joel C. Salomon]

Steven Schveighoffer wrote:
> I don't think such a series is definable with Andrei's template.  I think 
> his series template is only usable in situations where computing a[n] 
> depends only on n and the elements a[n-X]..a[n-1], where X is a constant.
> 
> I'm not really a mathemetician, so I don't know the technical term for the 
> differences, I'm sure there is one.


Time-invariant, or shift-invariant.