Page 677 - ExtendSim User Guide
P. 677

Analysis 651
Scenario analysis
block (Value library) which can be added to any model to control all aspects of the analysis. The Scenario Manager essentially keeps track of multiple what-if models, all based on the same model. It offers a highly flexible framework for experimentation and analysis.
The Scenario Manager is an advanced tool that is only available in the ExtendSim AT and ExtendSim Suite packages.
The ExtendSim Scenario Manager is a data storage and analysis system that supports analysts as they input, view, manage, and analyze various scenarios. It allows them to use a single model to explore and evaluate an unlimited number of options while providing precise control over model changes as well as easy access to the results. And it provides automated methods for quickly changing variable information and for generating scenario reports. It does this by assigning a named scenario to each combination of variables you choose to examine. For example, you can create best-, worst-, and typical-case assumptions for input values. Then recall each of these scenarios to see how the model behaves under different conditions. You can also recall scenarios in combination, such as best-case sales and worst-case costs.
The ExtendSim database is a central part of the Scenario Manager's data storage and organiza- tion. A database named Scenario DB is automatically created when a Scenario Manager block is added to the model. This database is used to store the inputs and results for the scenarios. The Scenario Manager also facilitates using a design of experiments (DOE) methodology for more efficient performance.
The Scenario Manager is one of three ExtendSim analysis tools; see “Comparison with other analysis methods” on page 664 for differentiators. While the Scenario Manager will meet the needs of most ExtendSim modelers, like most ExtendSim blocks it is open source. Thus a pro- grammer can modify and enhance it should the need arise.
How the Scenario Manager works
For scenario management you evaluate and compare a number of model configurations or sce- narios, where each scenario is one set of model inputs or factors. These factors are typically specific dialog parameters (such as the maximum number of items in an Activity) but can also be complete databases, tables, fields, or records. A scenario can have any number of factors and each factor can have any number, or levels, of different values that it can take on. (For example, setting the maximum number of items in the Activity to 2, 6, or 10 would be 3 lev- els.)
At the beginning of each set of simulation runs, or replications, the Scenario Manager copies the model factors for the current scenario into the appropriate locations in the model. Typically each scenario is run multiple times to capture any stochastic behavior. At the end of each of these replications, the results of interest (responses) are generated, recorded, and summarized. After all replications have completed, the scenario results are stored in tables in the Scenario DB database. You can also generate a report and export the data to a different ExtendSim data- base, an Excel workbook, JMP, Minitab, or a text file.
☞ It is best to set aside some time for all of the scenarios to run. Depending on the size and com- plexity it may take minutes to hours to complete the entire set of runs. You should also be care- ful not to create too many scenarios. This is particularly easy to do if you create a full factorial design.
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