Ordinary parameters (defined using the parm element) include switches, controls for pumps and drips, etc. Changes in the values of ordinary parameters do not cause a solution discontinuity and the solution can continue across solution segments.
Now consider an integrative physiology model where a gender parameter is toggled between male and female. With a gender change, the entire parameter space must be recalculated (resized) and it makes no sense to continue the solution in the presence of a large solution discontinuity. Instead, the solution is restarted and a new solution is undertaken.
Disruptive parameters are called context parameters (defined using the context element). An important part of this concept is that the values of context parameters are preserved across ordinary solution restarts (see below).
There are two types of solution restarts (as shown at the right in ModelSolver's popdown Redo menu).
An ordinary solution restart preserves the values of the model's context parameters. Ordinary parameter values are set to initial values, ordinary parameter dependent values are calculated, state variables (integrals) are set to their inital values and the solution is restarted.
A context restart sets the values of the model's context parameters to their initial values, context parameter dependent values are calculated and an ordinary solution restart (detailed above) is executed.
The scripting schema provides comparable restart elements.