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| <h1>Controlling scenario initialization by nesting models</h1> |
| <p>At the beginning of a simulation, STEM allows decorators such as population models, population initializers |
| and disease models to initialize themselves. For instance, when a disease model is initialized, it creates the |
| disease model labels necessary to track the state of the disese in a population. A disease model depends |
| on the population model labels created by a population model to be able to create the disease model labels. Furthermore, |
| a population model depends on the existance of static population labels, created either by a population initializers |
| or by dragging population data into your model from the STEM library. |
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| Consequently, the order of initialization becomes important, and the order is controlled by |
| nesting models inside models. Decorators that are deeper in the model tree are initialized before decorators higher up |
| in the tree. See the figure below for an example. Deepest in the tree is a population initializer that creates the |
| static population labels needed by the demographic population model one level up. The demographic population model |
| subdivides the population into subgroups needed by the disease model in the level above. |
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| In summary, the order is population initializers before population models, population models before disease models, |
| and disease models before infectors/inoculators. |
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| <img border="0" src="img/modelnesting.png""> |
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