Suppose you have a model which employs a deployment constraint to bolster the installation of a particular Resource, and you would like to see ‘behind the scenes’ of the calculation of the Resource Incremental Units result:
- Select Audit from the Resource icon menu in the Editor. The Resource Audit dialog is displayed, showing an empty list of Results.
- Select the list and double-click the --end of list-- item or press <Enter>. The Select Audit Results dialog is displayed, showing a full list of primitive Resource results (i.e., those stored by the model engine, as opposed to derived results which are calculated by the Results program when required). In addition to the familiar result names, there are a number of named features, prefixed with an asterisk, corresponding to specific stages of the model engine’s calculations.
Figure 1: Selecting audit results for a Resource
- Select Incremental Units from the list and click OK to close the dialog. The list of Results in the Resource Audit dialog is updated to reflect the selection.
- Select Save and Run from the File menu (or press <F5>). The model is saved and calculations commence. Almost immediately a STEM Model Audit window is displayed, showing pertinent data for whatever the first period is for your model. In this case, the audit reveals that, prior to the deployment calculation, there are 3 installed units, of which all are used; that demand has a One for One distribution over 13 sites; and thus that 13 units are required, which represents 10 extra units.
Figure 2: STEM Model Audit window for deployment
- Click Yes or press <Enter>. A similar window is displayed for Y1 (or whatever the next period is for your model), and so on.
If you wish to alter some relevant inputs or perhaps select another result:
- Click Cancel or press <Esc>. The audit is abandoned, leaving the Editor active.
Alternatively, if you have learned enough and wish to generate the remaining results:
- Click No. No further audit windows are displayed for this element. When the model run is complete, the audit is saved to a log file, and a message is displayed, offering you the opportunity to review the details.
Figure 3: Reporting the location of an audit log
- Click Yes or press <Enter>. The log file is displayed in the Windows Notepad.
Figure 4: Reviewing the details of an audit
Note: Once the audit log has been loaded into Notepad, the results are updated in the Results program in the background. Press <Alt+Tab> to switch to the Results program.
Introducing other effects
Suppose now you alter your model to give the Resource a utilisation constraint of, say, 80% by setting the input Maximum Utilisation =
0.8. Now when you run the model, you will see that the first audit window reports on the utilisation calculation, before the subsequent report on deployment, revealing not just the details of the utilisation calculation, but also the order in which the effects are calculated.
Figure 5: STEM Model Audit window for utilisation
Moreover, the model engine automatically reports on the features or stages of its calculations which directly affect a selected result, without you having to know in advance what those features are – which can be especially useful if you are auditing a model built by someone else.