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Model diagram elements : Initialisation


The Initialisation symbol is used to specify the initial number of individuals in a population submodel. It is sometimes called the Creation symbol, and belongs to the group of symbols known as channels. The symbol's icon represents the rising sun.

How to add an Initialisation symbol

The Initialisation symbol only has meaning in the context of a population submodel. Therefore, it makes sense to construct a population submodel first, then add the Initialisation to it. This is not strictly necessary: you can add the Initialisation first, then construct a submodel around it, then make the submodel into a population submodel, but it is better practice to construct the population submodel first.

See Adding node-type elements.


  • You can have any number of Initialisation symbols in any one population submodel. The initial population count will be the sum of their values. You may use more than one when the initial population consists of subgroups with different properties. You can use the channel_is( ) function on the initialisation channels to indicate which group each individual belongs to, and set its properties accordingly.
  • You do not need to have an Initialisation symbol in a population submodel. If you do not have one, then the initial number of instances for the population is zero. You would then have to have a migration symbol if you wanted your population ever to have any instances. (If you only had a reproduction symbol, then the population would never be able to get going, since reproduction only works for individuals already in the population.)
  • The Initialisation symbol may receive influence arrows, but (usually) only from variables calculated at the start of the simulation run, whose values do not change. A typical application would be to initialise the number of instances in the population from some fixed environmental attribute, such as the soil type or the area of the system being modelled.
  • It is possible to draw an influence arrow from the initialisation symbol to another element. The usual use of this is with the channel_is( ) function. Otherwise, the value of the initialisation symbol is always the number of individuals it caused to be created at the start of the run, even if the value of its expression changes as the model runs.​

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