

   SSaammpplliinngg TTiimmeess ooff TTiimmee--SSeerriieess

        time(x, offset=0)
        start(x)
        end(x)
        frequency(x)
        tsp(x)
        tsp(x) <- value

   AArrgguummeennttss::

          x: a time-series.

   DDeessccrriippttiioonn::

        `time', `start', `end' and `frequency' are generic
        functions with a `default' and a `ts' method (see
        `methods').  `tsp(x)' returns `c(start(x),end(x),fre-
        quency(x))'.

   DDeettaaiillss::

        `time' creates the vector of times at which a time
        series was sampled.  `offset' can be used to indicate
        when sampling took place in the time unit.  `0' indi-
        cates the start of the unit, `0.5' the middle and `1'
        the end of the interval.

        `start' and `end' extract the times the first and last
        observations were taken and `frequency' returns the
        number of samples per unit time.

        `tsp(x)' returns the vector `c(start(x),end(x),fre-
        quency(x))'.  It is included for compatibility with the
        S language.  In the assignment form, `value' must be a
        numeric of length 3 or `NULL' which removes the `"tsp"'
        attribute and the `"ts"' class of `x'.

   SSeeee AAllssoo::

        `ts', `window' and `system.time' for CPU usage.

   EExxaammpplleess::

        data(presidents)
        # a simple series plot
        plot(c(time(presidents)), c(presidents), type="l")

