External model tool

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Summary

Purpose

External model is a calculating piece of computer code that can be executed from within the toolbox, but it is physically outside the toolbox and it is maintained by a third party (not the user of the external model or the toolbox owner). This approach is utilised when 1) the model is unpractically large to be included in the toolbox, such as atmospheric dispersion models; or 2) the source code of the model is not freely available. The model looks like a function in the toolbox with the general format

  Variable = function(input parameter 1, input parameter 2,...),

where function is the external model and the input parameters are input values that are needed to run the model. The model is executed and the results retrieved using the variable transfer protocol.

Structure of the process

Procedure

External models are flexible in the sense that there is no need to restrict ourselves to a single software. However, this is only possible when:

• The software is able to take the data for the parameters (usually upstream variable results) from the result database, and
• The software is able to place the result of the variable into the result database.

However, parts of this information flow can, at least in the preliminary phase, be done manually.

Possible software that may have the required functionalities:

• Analytica, a Monte Carlo simulation program with graphical interface.
• R, an open access statistical software
• Unicorn (?), the "Uncertainty analysis with Correlations" (UNICORN) software tool, implementing staff research work on dependence modelling for high dimensional distributions.
• Many others if a module is built in the software to communicate using the variable transfer protocol.