Controlling Unscheduled Updates

In order to carry out a dynamic simulation, GoldSim steps through time in discrete intervals (referred to as timesteps). Calculations (referred to as updates of the model) are carried out at end of every timestep. Although the term timestep actually refers to an interval of time, it is often used interchangeably with the term update (indicating a calculation at a point in time). In GoldSim, there are two kinds of updates/timesteps: scheduled updates (or timesteps) and unscheduled updates (or timesteps).

Scheduled updates are specified directly prior to running the model. That is, you tell GoldSim when you want these updates to occur. Unscheduled updates are timesteps that are dynamically inserted by GoldSim during the simulation in order to more accurately simulate the system. That is, they are not specified directly prior to running the model. GoldSim inserts them automatically (and, generally, without you needing to be aware of it).

By default, scheduled updates are always dynamically inserted by GoldSim. However, in some (rare) cases, you may want to prevent unscheduled updates from being inserted. For example, if your model included a specialized algorithm that was designed based on the assumption that the timestep was constant, inserting unscheduled updates could invalidate the algorithm.

To support such situations, GoldSim allows you to disable unscheduled updates. You can do so by clearing the checkbox labeled Allow unscheduled updates (recommended):

Warning: Because unscheduled updates are intended to more accurately represent a complex dynamic system, disabling this feature should be done with caution, and is generally not recommended. In most cases, it will have the effect of deferring events to the next scheduled update, which under some circumstances could cause significant inaccuracies. In some cases (e.g., a Reservoir or Pool hitting an upper bound), its effects can be somewhat more complex (e.g., it changes how an overflow rate is computed). Some advanced features in GoldSim cannot function properly at all without using unscheduled updates. In these situations, GoldSim will throw a fatal error during a simulation if you have disabled unscheduled updates and are using such a feature.