Initializing intervals

Function: void ap_interval_alloc ()

Allocate an interval (with scalars of default type DOUBLE, the most economical).

Function: void ap_interval_free (ap_interval_t* op)

Deallocate an interval.

Function: void ap_interval_reinit (ap_interval_t* op, ap_scalar_discr_t discr)

Change the type of the bounds of the interval (mainly for internal use).