Date and Time

The command date returns the current date and time as a string.

> date();

If you prefer to know the number of seconds since 00:00:00 GMT, January 1, 1970 in seconds, then issue the rtime command (running time) with no arguments.

> rtime();

The rtime function can also except an expression as a parameter. In this form, rtime returns the time in seconds needed to evaluate this expression.

 for i from 1 to 100001 by 500 do
   lprint(i, rtime(factorial(i)));
 od;

As an aside, note that the running time does not grow linearly with the size of the factorial we are computing. This is because the built-in factorial function approximates the true value for large numbers using a variant of the gamma function (see § in Part  -The Reference Guide and [11]). Chapter  Measuring Performance explores this and related functions further.