Running Plays and forecasts

Machinations gives you three ways to inspect how a model changes: Play, Step and Forecast. Choose the control that matches the question you are asking.

• Play moves through the model step by step so you can watch its behavior.
• Step (the skip-forward button beside the step count; its tooltip carries your unit’s name) plays one step and pauses so you can inspect a particular state.
• Forecast compares outcomes across multiple Plays when a model includes uncertainty.

Play

Use Play to watch resources move and check whether the diagram behaves as you intended before you compare scenarios.

Play moves the model along on its own, one step after another, until it reaches the step count set in the Playbar beside Play (its menu is headed Steps per Play). Set that count before you Play: in the Willy Wonka example one step is a day and the campaign lasts two months, so the count is 60. The Speed control only changes how fast the animation moves, never the result. In the example this Play ends with $103 spent, over the $100 limit, so this Play does not reach the factory. But the number of bars bought each day is random (D5, one to five), so another Play can end differently. One Play is one possible path; use Forecast to see how often each outcome happens.

Step

Advance the model one step at a time when you need to see which component changed a value or why a particular state appeared.

Pause and reset

Pause to inspect a model in progress. Reset to return it to its starting state before trying another set of assumptions.

Forecast

Use Forecast to compare a range of possible outcomes. Its estimates depend on the rules and input values in your model, so keep those assumptions visible when you explain a result.

Forecast plays the model many times in the background and collects the results. Set the step count first, then choose the number of Plays in the menu beside Forecast (headed Plays per Forecast; the example uses 100) and press Forecast. In the Willy Wonka example, 29 of the 100 Plays collected the 10 golden tickets within the $100 limit by step 60, so the chance of visiting the factory is about 30%. That is what a Forecast is for: you can decide whether to spend the money, or raise the budget and Forecast again, with a number to look at instead of a single lucky or unlucky Play.

For current control details, read the Play modes documentation.