Simulistics

The File Parameters dialogue will contain entry fields for both fixed and variable parameters. Fixed parameters must be given a value; their captions in the dialogue will be shown in red until a correctly formatted value has been supplied. Variable parameters do not need a value, and can be left empty, so the value can be set by a slider while running the model. However, it is possible to enter a time series in the File Parameters dialogue, which will cause the variable parameter's value to be set at a series of specified time points while the model is running. You would normally set up the time series using the table data dialogue, but the direct method is described here to clarify the analogy with setting values for an array.

Entry format

The format for entering a time series is the same as for a one-dimensional array, except time points are given instead of indices. The time points can be REAL values, and do not have to be at regular intervals. Data for time point zero is loaded whenever the model is reset. So, to set a value five times between time 0 and time 100, the entry might look like this: 0 12 20 11 40 8 60 7 80 9

If the value to be set is an array, the data must specify a multi-dimensional array, with the time points as the outermost indices.

Special indices and values

The data for a time series can include two special indices: these are NOW and OTHERS. Data at time point NOW is loaded into the model as soon as the File Parameters dialogue is closed, and then not used again. Wiggling a slider effectively sets data at time point NOW. For time point OTHERS, you do not enter a value; instead, you enter one of the special values "use_last", "use_closest" or "interpolate". These select the different methods for getting a value when the time is not exactly equal to one of the indices provided. "use_last" specifies the default behaviour; each value stays in the model until the next time point is reached. "use_closest" causes the value to change midway between the two specified time points, while "interpolate" means the value changes continuously and linearly between one specified time point and the next. There is also another special value, "restart", which has a normal numerical time point as its index; this specifies a time at which the model starts reusing values at the beginning of the time series, starting with time 0. The value will then follow a regular pattern, whose period is the time index of the "restart" value. The time for "restart" must be the last in the sequence, with OTHERS being second last if both are specified.

Example: rough approximation of sinusoidal variation with period 100 time units:

0 0 12.5 0.7 25 1 37.5 0.7 62.5 -0.7 75 -1 87.5 -0.7 OTHERS interpolate 100 restart

When entering time series values in the table data dialogue, there are special buttons to get these behaviours by setting the special indices and values.