Modifying How Integrators Treat the Rate of Change

By default, the Rate of Change at time t is treated as the constant rate of change over the next timestep A discrete interval of time used in dynamic simulations. (i.e., from t to t + Δt). In some very special cases, however, you may actually want GoldSim to treat the Rate of Change in a different manner. In particular, you may want to modify this behavior such that the Rate of Change at time t is treated as the constant rate of change over the previous timestep (i.e., from t to t - Δt).

The most common reason for doing this is when you want to use an Integrator to integrate a mass flux coming from a pathway element in the GoldSim Contaminant Transport Module. Pathway elements output mass flux rates that represent rates over the previous timestep. Therefore, in order to correctly integrate such a flux, an Integrator element An stock element that integrates rates. would need to treat the Rate of Change as if it represented the rate of change over the previous timestep.

GoldSim provides an option to allow Integrators to treat the Rate of Change in this way. By default, the option is deactivated. To activate it, you must press the More button to expand the dialog:

By default, the checkbox labeled Rate of change applies to the PREVIOUS time step is cleared. If you check this checkbox, the Integrator element will treat the Rate of Change as if it represented the rate of change over the previous timestep.