Compute indices of reference value using Date class
The reference values are formed based on computations
seq for Date class arguments.
A Date object describing the time point
Number of years to go back in time
Half width of window to include reference values for
Vector containing the epoch value of the sts/disProg object
Using the Date class the reference values are formed as follows:
t0 go i, i= 1,...,
b years back in time.
For each year, go
w epochs back and include from here to
w epochs after
In case of weeks we always go back to the closest Monday of this date. In case of months we also go back in time to closest 1st of month.