By default, Stochastic elements are sampled once per realization (when their parent Container is first activated, which is typically at the beginning of the realization).
Stochastics can also be triggered to resample themselves by events. This may be useful, for example, if you wanted to resample a parameter representing the value of a discrete change (e.g., the magnitude of a storm) every time a particular event occurred, or if you wished to generate stochastic time histories (e.g., a precipitation record) by sampling a Stochastic on a regular basis (e.g., every day).
The Resample… button in the Stochastic dialog provides access to a standard Trigger dialog for controlling when a Stochastic is sampled:
By default, Sampled once is selected and this button is grayed out. This implies that the element will be sampled only at the beginning of the simulation.
If you select the Resampled radio button, the Resample... button becomes available, and you can define one or more triggers.
Note: If the
Stochastic is not contained within a conditional Container, or if it is
contained in a conditional Container but is static (i.e., no triggers are
defined and is not otherwise a function of time), it will automatically be
sampled at the start of the realization (and never again). If it is
contained in a conditional Container and is not static (i.e., has at
least one trigger defined or is otherwise a function of time), it is
automatically sampled when its parent Container activates, and is assigned a
value of zero prior to activation of the Container
Note: One common
requirement in models which represent a time-variable or stochastic process is
to resample a Stochastic on a regular basis (e.g., every day or every month).
You can do this in an easy way by utilizing the various Run Properties. For
example, defining an On Changed trigger as “Day” would force the Stochastic to
be triggered every day.
Note: If Stochastic X is correlated
to Stochastic Y, you cannot specify that X is to be resampled (a Stochastic that
is correlated can not be explicitly resampled). However, if Stochastic Y is
resampled, then Stochastic X will also automatically be resampled (although this
is not explicitly indicated in the dialog for X).
Learn more about:
Understanding Event Triggering