Inertial delay is the default delay type if a signal assignment
statement contains an after clause. This delay model assumes
that a signal in a device has a certain amount of "inertia" that must
be overcome before the signal can assume a new value. By default, this
inertial delay is equal to the propagation delay time of the device.
If the signal is of shorter duration than the inertial delay, then the
pulse will not be seen at the output.
In the example above, the (inverted) value of the signal Input
will be assigned to the signal Output AFTER 10 ns. Because
inertial delay is the default, it does not need to be specified
explicitly. In the example waveforms above, the 10ns inertial delay
on the inverter will suppress the 5ns pulse on Input from being
propagated to Output. That is, Output cannot have any
pulses smaller than its inertial delay. Note that the Input's
change at time 20ns is long enough to propagate to Output.
