Flowsheet Optimizer Advanced Options

The Optimizer Advanced Options are intended for use by experienced users of PRO/II. If you are unsure of how these features apply to your simulation, consult SIMSCI Technical Support or refer to the PRO/II Reference Manual.

Access

Navigate from the optimizer main window by pressing the Options button to display the Optimizer - Options DEW. From there, press the Advanced Options button.

Special Line Search Logic

This option is used to enable a line search mode method for the optimization calculations. By default, this feature is Off. Selecting Specified Number of Trials from the drop-down list box enables this feature.

When this feature is enabled, you may specify the maximum Number of Line Search Trials for any one optimizer cycle. The number specified must be an integer greater than or equal to 1.

Number of Independent Variables to Eliminate

You may specify the number of independent variables to be eliminated during the solution of the optimizer calculations.

Start Broyden Updating at Cycle

The optimization cycle at which Broyden Updating will begin. By default, this option is Off. Specify a positive integer to enable this feature. The specified integer must be 2 or greater.

Derivative Analysis

By default, this option is Off. Select On from the drop-down list to enable this feature. When enabled, this option generates derivatives of each variable. The variable is perturbed above and below the current value, and derivatives are derived by finite difference. A report of the analysis lists derivative step sizes for each optimizer cycle, and suggests a modified perturbation step size, when appropriate.

Limit Optimization Step Sizes

By default, this option is enabled (Yes). When enabled, this option limits the step sizes taken by the optimizer to 30, 60, and 90 percent of the upper or lower bounds during optimization cycles 1, 2, and 3, respectively. This is intended as a safety feature; it prevents the optimizer from moving too far, particularly when the derivatives are inaccurate.

Selecting the No option in the drop-down list box disables this feature.

Separate Shadow Price Output File

Once the flowsheet optimization has converged and the appropriate operating conditions have been determined, the shadow prices or Lagrange multipliers can be used to assess the sensitivity of the objective function to the specifications, constraints and bounds.

For maximization problems, a positive shadow price indicates that the constraint is being pushed against its upper bounds. A negative shadow price indicates the lower bound is still active. A zero shadow price indicates that the constraint does not affect the solution.

By default, printout of these values is disabled (selection of the None option in the Separate Shadow Price Output File option drop-down list box).

Selection of the Brief option produces a separate output report with the same file name as the input file (with a .SHD extension). This report contains the id’s of the variables, specifications, and constraints. These and their corresponding shadow prices appear as part of the standard output report.

Selection of the All option produces a separate output report with the same file name as the input file (with a .SHD extension). It contains a detailed summary of the final optimizer solution. This summary includes the values of the objective function, all variables, specifications, and constraints. Also included are the shadow prices for all active bounds and constraints.

Complete technical details may be found in topics under Flowsheet Solution Algorithms in the PRO/II Reference Manual.

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