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| Decision variables | The management levers which can be pulled in order to achieve the required objectives. Each decision variable must be defined as a global expressionFunction, with an allowable range of values it can take. |
| Dominated solution | When comparing results from two Source runs (or group of runs), ‘A’ and ‘B’, Insight will treat ‘A’ as a “dominated solution” only if it is clearly inferior to ‘B’; that is, if ‘B’ performs better than ‘A’ on at least one of the statistics and there is no statistic where ‘A’ performs better than ‘B’. In this case ‘B’ is a “non-dominated solution” and is a potential candidate for the Pareto front of optimal solutions (e.g. see Figure 1). |
| Generation | For each generation the decision variables are subject to selection, crossover and mutation. The number of generations is specified by the modeller. |
| Individual | A solution obtained from a single run of Source with a given set of decision variable values (an individual is a group of runs when multiple scenarios are being investigated: one run for each scenario). |
| Non-dominated solution | See definition of “dominated solution”. |
| Objective function | Mathematical expression of the objectives required to be achieved (e.g. minimising the operating cost of the system, maximising environmental benefits, or minimising time spent in water restrictions). Objective Functions are set up as global expressions Functions within Source. Note that only the value of the expression Function at the last time step is used for evaluating the objective function. Therefore, expressions Function should be defined in such a way that the value at the last time step of the simulation is the value that represents the required statistic for the entire simulation period. |
| Population | The number of possible feasible solutions to be derived by changing decision variable values (within their value constraints) in Insight and running Source. The population size is specified by the modeller and is equal to the total number of individuals. |
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The functionality listed in Table 1 is all concerned with input and output data handling and how Insight and Source interact, and there is no new science involved. Therefore, the functionality in Insight is not discussed further here and reference should be made to the Insight: Objective Multi-objective optimisation for information on how to use it.
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The decision variables and objective functions must be defined in the Source project as global expressionsFunctions. Hence, in order for a Source parameter to be included in an optimisation problem, that parameter needs to be able to be defined through the expression Function editor.
More details on data are provided in the Source User Guide.
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