MMP.18:1 - Problem frame

Use this pattern when the required answer combines models whose shared quantities, representations or scales differ. One model may return an average while another needs a distribution. Two simulations may exchange a flow at different times. Two statistical analyses may reuse the same prior or observations.

Begin at one exchange that affects the answer. Identify what the supplying model returns, what the receiving model uses it to mean, and the relation needed to connect them. A matching variable name or software interface leaves that relation to be constructed.

The result is a joint formulation: component models with their shared quantities, interface relations and the assumptions needed to use their combined answer. It may expose a missing closure, incompatible conditions or a dependency that an available simulator cannot realize. The first useful result can be that obstruction, or a restricted coupled answer sufficient for the work.

This is mathematical coupling across models. A.3.3.TR supplies joint relations and change rules; MMP.10 supplies their constraint formulation. The additional work here constructs exchanges between representations, preserves the quantities the use depends on, and accounts for shared information. Subject methods supply the meaning and applicability of those exchanges.

The reader needs the mathematics used by the components and their connection. Algebra suffices for the first coupling steps; time-dependent, spatial or probabilistic branches require the corresponding integration, mapping or probability knowledge. A collaborator can construct the mathematics from supplied models and a recoverable subject question.

Use an already adequate joint model directly. Merely keeping several alternative models in a portfolio does not require coupling them into one model. Use portfolio and improvement methods when the alternatives serve complementary questions without exchanging modeled quantities or information.