PHY.5:4.3 - Choose how unresolved processes enter the retained account

Select the variables and interactions needed by the consequence. They may describe individual participants or collective quantities such as a displacement field, concentration or slowly changing amplitude.

For a part that adjusts rapidly, first determine what it adjusts to. Substitute that response into its coupling with the retained part. The resulting force, constraint or transport remains in the effective account. In the motor example, eliminating rapidly changing current retains its effect on torque and damping.

For a collection of unresolved processes, determine which of their effects remain:

• a mean response changes the retained forces or transport coefficients;
• a delayed response makes current change depend on earlier states;
• fluctuations produce a spread of possible changes around a mean response;
• a persistent unresolved mode may require another retained state.

Choose among these from the physical preparation and interactions. Eliminating variables mathematically can expose a memory term even in deterministic dynamics. A statistical description additionally needs grounds for the distribution of unresolved states. MMP.7 supplies probability composition for a specified information and recording situation; it does not choose the physical preparation.

An effective coefficient can be obtained from a more detailed description, existing measurements or a constrained response law. Compare the predicted quantity in a regime where the two descriptions apply and choose the coefficient to preserve that contribution. This matching can be useful even when no complete microscopic theory is available. Carry the range and remaining uncertainty that change its later use.