To set Crystal Ball run preferences, select Run Preferences in the Oracle Crystal Ball ribbon. For optimization purposes, you should usually use the following Crystal Ball settings:
Trials tab — Maximum number of trials to run set to 1000.
Central-tendency statistics such as mean, median, and mode usually stabilize sufficiently at 500 to 1000 trials per simulation. Tail-end percentiles and maximum and minimum range values generally require at least 2000 trials.
Sampling tab — Sampling method set to Latin Hypercube with the default bin size.
Latin Hypercube sampling increases the quality of the solutions, especially the accuracy of the mean statistic.
Sampling tab — Random Number Generation set to Use Same Sequence Of Random Numbers with an Initial Seed Value of 999.
The initial seed value determines the first number in the sequence of random numbers generated for the assumption cells. Then, you can repeat simulations using the same set of random numbers to accurately compare the simulation results. If you do not set an initial seed value, OptQuest will automatically pick a random seed and use that starting seed for each simulation that is run.
When your Crystal Ball forecast has extreme outliers, run the optimization with several different seed values to test the solution’s stability.
After you define the assumptions, decision variables, and forecasts in Crystal Ball, you can begin the optimization process in OptQuest.