Vensim has two methods to set up optimizations: from the Optimization button on the Toolbar, and from the Simulation Control.
In calibration optimization, the payoff defines which variable(s) you are trying to fit. Payoff files have the extension .vpd (Vensim payoff definition) and by default have the same name as the model (e.g., electric.vpd for this model).
| Ø | Double click on the simulation Runname editing box and type a name for the dataset, e.g., run2. |
| Ø | Click the Optimization button  on the Toolbar. The Optimization Wizard opens with the Payoff Definition active. |
| Ø | Click the "Add" button to add a new payoff element. |
| Ø | Make sure the Calibration radio button is selected. |
| Ø | In the Variable editing box, type in percent of US dwellings with electric power (or use the Sel button to select it). In the Weight editing box, type in the number 0.25. Click the "OK" button. |
| Ø | Click the "Add" button to add a new payoff element. |
| Ø | Make sure the Calibration radio button is selected. |
| Ø | In the Variable editing box, type in US population (or use the Sel button to select it). In the Weight editing box, type in the number 3E-7 ( 0.0000003). Click the "OK" button. |
The weights act to balance the numerical sizes of the different variables. Because the optimizer is only looking at pure numbers, variables with larger values are given more importance than those with smaller values. The numbers assigned to weights are based on both the confidence we have in the data, and the units of measurement. percent of US dwellings with electric power has values around 50 and a weight set to 0.25. US population, which has a number around 200 million, has a weight that is much smaller (30 / 100 million). These weights were chosen to be approximately equal to the one over the standard deviation of the prediction error on these variables. Optimization in the Reference Guide contains more discussion on the meaning of these weights.
This is how the dialog looks when creating a new payoff element
This is how the dialog looks when both payoff elements have been created
| Ø | Click Next to move to Optimization Control. |
