Configuring the Optimization Variables

You can select the parameters that will be used as variables during execution. The list of parameters on the Variables subtab includes all input and in/out parameters from the Six Sigma component and input and in/out parameters from the subflow components, if they are not mapped to any parameters of the Six Sigma component. In addition, the list of parameters includes the standard deviations of Six Sigma random variables that can be used as design variables to drive the standard deviations as exposed tolerance variables.

  1. Double-click the Six Sigma component icon .

    The Six Sigma Component Editor appears.

  2. From the Six Sigma Component Editor, click the Optimization tab.

  3. Click the Variables subtab.

  4. Right-click in the table to access various options for working with variables.

    For more information, see Setting Table Options.

  5. Perform the following actions, which may vary based on your model design:

    1. Determine which parameters you want to use as variables by selecting the corresponding check boxes in the first column. Alternatively, you can click Check to add all the selected parameters (including array elements) as design variables. To clear all the parameters, click Uncheck.

      If no parameters are selected, you will be prompted to add all parameters as design variables.

      You can select standard deviations as design variables. Selecting standard deviations creates an aggregate that contains only the standard deviations. The values that you specify will override any attribute mappings.

      Selecting a subflow parameter as a variable creates a corresponding parameter in the Six Sigma component and Optimization component when you click OK or Apply. You can select only real, integer, and string parameters.

    2. Specify the Lower Bound for the variables in the corresponding column. This setting is required if you are using the automatic scaling component preference. For more information, see Setting Optimization Component Preferences.
    3. Change the initial value in the Value column.

      Note: This column is not available for the Multi-Island Genetic Algorithm because the initial design point is not used by this algorithm.

      Warning: The initial values of the variables are overridden at execution time if the Optimization component is a child component of another process component (e.g., a Task component). Therefore, to change the initial values of variables, you must change the corresponding parameter values in the parent (Task) component.

      Changing initial values of variables changes their values in the main Design Gateway window. These changes are immediate and cannot be reversed by clicking Cancel on the Six Sigma Component Editor.

    4. Specify the Upper Bound for the variables in the corresponding column. This setting is required if you are using the automatic scaling component preference. For more information, see Setting Optimization Component Preferences.
    5. Type a list of allowed values in the Allowed Values column, separated by a semicolon. If you enter allowed values, the lower and upper bounds are erased, and vice versa. Entering a list of allowed values creates a discrete variable, and the Six Sigma component will use only these values during optimization. The optimization algorithm will view this variable as an integer parameter with the range of values 0, 1, 2, …, N−1, where N is the length of the allowed values list.
    6. Set the Scale Factor for the variable in the corresponding column. Scale factors are used to bring variable values to the same order of magnitude to improve the efficiency of the optimizers.

      Note: This column does not appear if you use the automatic scaling component preference. For more information, see Setting Optimization Component Preferences.

    7. (Multi-Island Genetic Algorithm technique only) Set the value in the Gene Size column. This value controls the number of bits N in all genes used for encoding the value of each variable. Every bit of the gene can change its value between 0 and 1. The total number of possible combinations in every gene is then 2N. This number of combinations determines the minimum change in the value of any design variable during all genetic operations—take the allowed range of values for a design variable, and divide it by the total number of combinations. To increase the minimum change in design variable values (i.e., to decrease the number of possible bit combinations when the allowed range of design variable values is small), decrease the gene size.

  6. If desired, click Edit at the bottom of the editor to set attribute values for multiple design variables.

    For more information, see Editing Attributes for Multiple Parameters.

  7. If desired, map any of these variable attributes to parameters.

    For more information, see Mapping Options and Attributes to Parameters.

  8. Click OK to save your changes and to close the Six Sigma Component Editor.

    When you select Six Sigma Optimization and click OK or Apply for the first time, the model is modified by embedding the Six Sigma component under an Optimization component. All optimization criteria are copied to the Optimization component and all selected parameters will be mapped up to the Optimization component. You can still edit the optimization criteria in the Six Sigma Component Editor.