Using Groups to Write Model Constraints

Adding model constraints often requires us to take advantage of Cosmic Frog’s Groups feature. Using the Groups table, we can define groups of model elements. This allows us to reference several individual elements using just the group name.​

In the example below, we have added the Harlingen, Ashland, and Memphis production sites to a group named “ProductionSites”.​

Now, if we want to write a constraint that applies to all production sites, we only need to write a single constraint referencing the group.

 

 

 

When we reference a group in a constraint, we can choose to either aggregate or enumerate the constraint across the group.​

Aggregating constraints across a group

If we aggregate the constraint, that means we want the constraint to apply to some aggregate statistic representing the entire group. For example, if we wanted the total number of pens produced across all production sites to be less than a certain value, we would aggregate this constraint across the group.​

 

 

Enumeration constraints across a group

Enumerating a constraint across a group applies the constraint to each individual member of the group. This is useful if we want to avoid writing repetitive constraints. For example, if each production site had a maximum production limit of 400 pens, we could either write a constraint for each site or write a single constraint for the group. Compare the two images below to see how enumeration can help simplify our constraint tables.

Without enumeration:

 

With enumeration: