Change the independent status of a variable in an Optimization Set

A well-posed simulation will have a locally unique solution if it has the same number of equations and calculated variables. However, if the simulation has more calculated variables than equations, there are an infinite number of solutions from which an Optimizer can choose the "best" one (for example, the one that maximizes profit). We call these extra variables "Independent" or "Independent and calculated."

You can use the Independent flag on the Optimization Set Editor to define the Independents. AVEVA Process Simulation automatically sets specified variables as Independents when you add them to the Optimization Set. You can change the Independent status for any specified variable in the Optimization Set. When the variable is an Independent, AVEVA Process Simulation manipulates this ordinarily-specified variable to help achieve the desired optimization.

You should not set calculated variables as Independents. If you do, an error badge appears that indicates the discrepancy.

The specified and calculated status for variables may change based on the simulation mode. You may need to change the variables that you set as Independents based on the simulation mode or create similar Optimization Sets with different Independents for each simulation mode. For example, by default, the mass flow, W, of a Source is specified in Process mode and calculated in Fluid Flow mode. If you set W as an Independent in an Optimization Set, you can run the Optimization Set in Process mode but a warning appears if you try to run the Optimization Set in Fluid Flow mode.

Change the independent status of a variable in an Optimization Set

1. Open the Optimization Set Manager.

2. Select the Optimization Set that contains the variable that you want to change, and then select Edit. The Optimization Set Editor appears.

3. Expand the Variables section if it is not already visible.

4. In the Independent flag column, select the flag icon for the variable.

   A colored flag icon indicates that the ordinarily-specified variable is an Independent for an optimization run.

   A gray flag icon indicates that the variable should behave as it does outside of an optimization run. For example, if the variable is calculated in the current simulation mode, it remains calculated in the optimization run. If it is specified in the current simulation mode, it remains specified during the optimization run.