Where a parameter cannot be defined using a function using the main user interface, adding usages manually allows you use a function to define almost any parameter in the model. For example you can make otherwise static parameters change over time like rainfall runoff parameters.
When a function is used in a model (in an inflow node for example), then that usage is shown in the tree under the function. If a function is used in multiple places, then all usages are shown under the function in the Function Manager tree.
Suppose you want to calibrate the storage routing exponent (m) on one of the reaches in a Source model.
- Initially, identify which link or node in the model you want to place the expression in.
- Then, add a function in the node/link feature editor;
- Exit the node/link feature editor;
- In the Function manager, first assign a value to the function. Right click, then choose Edit function. Note that the function units are assumed to be the same as that in the underlying code. As a guide, rainfall-runoff models generally use millimetres for length and day for time-step and the groundwater model uses SI units - metres for length and seconds for time-step;
- Back in the Function manager, right click on the required function again and choose Manually add function usage; and
- Then add the function usage manually to allocate a parameter to the variable (steps outlined in Figure 1). You can now use the Command Line Runner to run the model iteratively while varying the parameter. This is also used for setting up a project to run with Insight: Objective optimisation.
Figure 1. Adding Function Usages Manually
