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# Genetic algorithm parameters in Darwin Designer

 Applies To Product(s): Bentley WaterGEMS Version(s): 08.11.xx.xx Environment: N/A Area: Modeling Subarea: Original Author: Scott Kampa, Bentley Technical Support Group

# Problem

How do the different genetic algorithm parameters, found in the Option tab for the automated design, work in Darwin Designer?

# Solution

The genetic algorithm parameters are used to control the underlying algorithm used in the optimization process. The Help topic entitled "Advanced Darwin Designer Tips" contains some useful information on the nature of these parameters.

In general, the most common parameters for a user to change, would be simply population size and random number seed.

### Random Seed:

All other variables (and input) being the same, using the same random number seed produces the same optimized result(s). Because of that, it is sometimes necessary to change the random number seed in order to test the sensitivity of the random starting population to the solutions of the problem being optimized. If changing the random number seed has little effect on results, then you can be fairly confident that the optimization is converging and additional runs will likely yield negligible benefit. If changing the random number seed results in very different results (in terms of fitness) then it may be that the problem needs to be run longer or that the optimization has a configuration problem of some kind.

### Population Size:

With GA optimization having a stochastic nature it may be beneficial to vary population size up or down. Using a smaller population size will result in faster runs, but with less population diversity and potentially less optimized results. However, it may be useful way to debug runs more quickly when initially configuring your optimization problem. Using a larger population size will increase the initial population and genetic diversity so that in theory there is a higher chance, that through having more random starting points, one of those starting points will be very beneficial to the overall optimization. The downside is that the optimization run will take longer to execute and converge.

### Other GA Parameters:

Generally, most users will not want or need to change other variables as they have already been set to good defaults. The impact of changing these parameters will tend to be pretty minor.

# See Also

Using Darwin Designer

• Created by
• When: Fri, Nov 20 2015 3:44 PM
• Revisions: 1
• Comments: 0
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