Calculations

The Constraints and Alerts page shows calculations inherited from the source cases used to define the per-period settings for each plant.

Follow these steps to create a new calculation:

1. From the Calculations group of the Home ribbon tab click Add Calculation. The Create New Calculation dialog box opens.

2. Enter a Name for the calculation.

3. Optionally, choose a Type for the calculation. See Calculation types for more information.

4. Choose a Start Period and an End Period for the calculation. The start period is the first period in which the calculation is applied, either a specific period or the special designator First which is defined as the first active period. Similarly, the end period is the last period in which the calculation is applied, and you can use the Last designator for the last active period.

5. Optionally, select the unit of measure of the calculation result. First choose the appropriate UoM Category, then choose the UoM itself.

   Tip: If you do not enter a unit of measure, when you write the calculation formula Network alerts you that the final UoM is incorrect, and allow you to set it based on the result of your calculation.

6. Click the button to choose one or more variables to use in your calculation. See Variable Types for more details. Based on the variable type you choose from the menu, a different dialog box opens, allowing you to define all the parameters of the variable.

7. Once all the variables are defined, write the formula defining the calculation result in the Formula text area. If there are any errors in the definition, such as misspelled or unknown variable names, the expression parser highlights the potential errors.

   Tip: See Writing Formulae for more information on the correct syntax and available operators for writing formulae.

   If the calculation result is not compatible with the unit of measure you have selected for the calculation, or if you have not selected a unit of measure, a warning appears at the bottom of the window. A button under the UoM drop-down menu allows you to set the calculation unit of measure to a compatible value.

8. Optionally, open the Constraints tab and enter any of the following:

   • Either a minimum and/or maximum Constraint value that the calculation results cannot exceed, or a Fixed value that the calculation result must meet.

   • A minimum and/or maximum value that results in a Warning being generated if the calculation result exceeds the allowed range.

   • A minimum and/or maximum value that results in an Error being generated if the calculation result exceeds the allowed range.

     Note that you can also enter these values in the Constraints and Alerts page, after you have added the calculation.

9. Optionally, enter a description for the calculation in the Description tab. As with the constraints, you can also do so in the Constraints and Alerts page, after you have added the calculation.

10. Click OK. The Create New Calculation dialog box closes and the calculation is added to the table in the Constraints and Alerts page.

Use the calculation editor

The actual formula used to define how the calculation is determined is entered on the Formula tab. The formula is written using standard mathematical notation and operators (Writing Formulae) using variables which relate to values within the supply chain model.

The Formula tab is divided into two panes. The upper pane lists the variables you have defined. The lower pane is where you write the actual formula. When you start typing into this pane, a tooltip appears with a list of matching variable symbols. Click on a symbol to add it to the formula.

To resize the two panes, move the mouse pointer to the gap between them until the pointer becomes a horizontal line with two arrows (). Then click and drag to resize.

Add variables. To add a variable to the calculation, click the button and choose the relevant Variable Type. Variables are usually associated with particular assets, so choosing the variable type is an important step in defining the exact asset and conditions whose variable value should be used in the calculation.

Tip: When adding a new variable, the value of fields in the dialog window is based on the currently selected variable.

Duplicate variables. Click the icon to create a duplicate of the selected variable. You will have to change the symbol of the new variable to be different from that of the other variable.

Edit variables. Click the icon to edit the selected variable.

Remove variables. Click the icon to remove the selected variables. You can select and delete multiple variables at a time.

Edit linked calculations and constraints

Where multi-period runs are being performed, period specific-configurations are entered using cases. You can review per-period per-plant calculations in the Constraints and Alerts grid and edit constraining values directly in the multi-period workspace.

Note: Editing the constraint value for the calculation edits the value for the underlying case. If this case definition is shared across multiple periods, the new value is applied to all these periods.