start(x, …)
end(x, …)start and end has no
meaning unless the frequency is supplied.tsp attribute of x if it exists.
Their default methods decode the start time from the original time
units, so that for a monthly series 1995.5 is represented
as c(1995, 7). For a series of frequency f, time
n+i/f is presented as c(n, i+1) (even for i = 0
and f = 1).ts, time, tsp.