Use when simulating with no intervention or a simple intervention.
The rule of thumb to keep in mind with this function is that
the timing of all events and observations is determined prior to
the model run. This has particular consequences for infusion
duration and lag times that might be set in $MAIN.
Specifically, bioavailability is implemented for bolus but not
infusion doses. Infusion rates and durations are not modeled
from $MAIN. Dose lag times are not modeled
from $MAIN. If these features are needed or when in doubt,
use mrgsim.