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The NonlinearInteraction can be used by itself or in combination with the →LinearInteraction flow to model more complex interactions. The netflows to the connected stocks A (portA) and B (portB) are given by the following equations:

Note: Capital letters were chosen to represent the stocks (state variables) connected at portA and portB in the formula above. Also dot notation is used for a stock's rate of flow—its first derivative with respect to time.

Coefficient	Unit	Description
a_AB	1 per second per base unit of B (TypeB)	Factor used to determine the net flow to A (positive rate = inflow)
b_AB	1 per second per base unit of A (TypeA)	Factor used to determine the net flow to B (positive rate = inflow)

The coefficients can be given as parameters or as variables via the expandable connector dataIn.

Examples

A nonlinear component is typically found in predator-prey models or models of infectious diseases, where the exponential growth rate for a population depends upon the size of another population (e.g., prey or susceptible population).

Notes

• When this component is used with stocks that have "simple" units, e.g., Amount [each] then it is rather straight forward to enter a fractional rate per unit of A or B for the parameters a_AB, b_AB and we can in fact leave TypeA, TypeB, refA, refB at their default values.


• In cases, where we want to specify a fractional rate per some displayUnit for one of the stocks, we can use the type selectors TypeA, TypeB to select the appropriate units for the connected stocks and then set the references values refA, refB using whatever displayUnit we want.

See also

LinearInteraction, ComplexInteraction

a_AB	Value: unspecified Type: Rate (1/s) Description: Constant fractional rate for the netflow to A per unit of B (nonlinear coupling factor)
refB	Value: 1 Type: TypeB Description: Reference value for B, i.e., divisor for the fractional rate a_AB
b_AB	Value: unspecified Type: Rate (1/s) Description: Constant fractional rate for the netflow to B per unit of A (nonlinear coupling factor)
refA	Value: 1 Type: TypeA Description: Reference value for A, i.e., divisor for the fractional rate b_AB
hasConstantFactorA	Value: false Type: Boolean Description: = true, if the coupling factor for A is given by the constant parameter
hasConstantFactorB	Value: false Type: Boolean Description: = true, if the coupling factor for B is given by the constant parameter

• InputConnector defined as encapsulated expandable connector in v2.1.0.


• Values for optional parameters changed to unspecified in v2.1.0.


• Adapted types and added divisors for unit compliance and convenience in V2.2.