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Running models

Running models

Once you have drawn the model diagram and specified how to calculate the value of each element, you are ready to perform a simulation. During the simulation, the model is run for a specified number of time steps, and the changing values of any of the elements can be plotted, recorded in tables, or displayed using a variety of other visual tools. You can develop your own displays specific to the needs of your models.

Preparing models to run

Before it runs a model, Simile generates an executable program from the model diagram.

Diagnostic messages

How Simile interacts with the modeller to display and correct problems

Run time environment

Simile provides two alternative environments for running models and seeing the results of the simulation. The standard one uses a single window containing a number of panels: one for controlling the simulation, another for any input sliders, and others that can contain graphs or other ways of visualising model behaviour. The alternative, multiple-window environment has a separate window for each of these.

You decide which of the two run-time environments you want by ticking or un-ticking the option "Single-window Model Run Environment" in the Preferences dialogue window, obtained by selecting the Preferences item in the Edit menu.

As of Simile v6.12 it is possible to have a browser window display the status of the running model.

Controlling model execution

Whichever execution environment you choose, you control the model's execution via the run control panel. This is either a special box within the single execution window, or a whole window itself, but looks the same in either case. It allows you to:

  • start, pause and reset the model's execution,

  • set the time for which it will execute and the frequency of display updates, and

  • adjust other execution variables such as the step size and integration method.

Visualising model behaviour

The term "helper" is the generic term in Simile for any tool for displaying model behaviour (i.e. the values for variables), or for entering values into a running model.

Parameter estimation and predictive analysis

Simile incorporates an interface to the PEST parameter estimation tool. This carries out parameter estimation by varying model parameters in order to match model behaviour with measured data from the system being modelled. It can generate prediction ranges for model outputs based on combinations of parameter values found in this way.

Working with external data

If your model has variables whose data source is chosen as being from file, i.e. so-called "file parameters", then it requires data to be provided before the simulation can proceed. A file parameter dialogue window will appear to enable you to provide the required information.

Scripting model execution

In addition to the interactive run-time environments, a scripting interface is provided to enable simulations to be run without user interaction. This is often useful for simulation experiments, e.g. running the same model for a set of scenarios (probably defined by parameters in a scenario file), for sensitivity analysis or parameter estimation.

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