LotkaVolterraThe LotkaVolterra equations to model predatorpreydynamics 
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These are the classical LotkaVolterra equations describing predatorpreydynamics in an idealized way [17]. The dynamics for the prey population (portA
) and the predator population (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 flowâ€”its first derivative with respect to time.
Coefficient  Unit  Description 

alpha 
1 per second 
fractional growth rate for prey population 
beta 
1 per second per base unit of B ( TypeB ) 
fractional rate of decline for prey population per predator 
gamma 
1 per second 
fractional rate of decline for predator population 

1 per second per base unit of A ( TypeB ) 
fractional rate of groth for predator population per prey 
LinearInteraction
and NonlinearInteraction
the rates passed for a_B, a_AB, b_A, b_AB
call for divison by a reference level of the connected stocks. In many cases, modelers can leave the type selectors TypeA, TypeB
at their default value of Unspecified
so that no conversion will take place.displayUnit
settings to enter convenient reference levels refA, refB
.refA 
Value: 1 Type: TypeA Description: Reference value, i.e., divisor, for the couplings b_A, b_AB 

refB 
Value: 1 Type: TypeB Description: Refrence value, i.e., divisor, for the couplings a_B, a_AB 
alpha 
Value: unspecified Type: Rate (1/s) Description: Fractional growth rate of prey population (A) 
beta 
Value: unspecified Type: Rate (1/s) Description: Fractional rate of decline for prey population (A) per predator 
gamma 
Value: unspecified Type: Rate (1/s) Description: Fractional rate of decline for predator population (B) 
delta 
Value: unspecified Type: Rate (1/s) Description: Fractional rate of growth for predator population (B) per prey 
hasConstantAlpha 
Value: false Type: Boolean Description: = true, if the constant parameter value is to be used instead of the input connector 
hasConstantBeta 
Value: false Type: Boolean Description: = true, if the constant parameter value is to be used instead of the input connector 
hasConstantGamma 
Value: false Type: Boolean Description: = true, if the constant parameter value is to be used instead of the input connector 
hasConstantDelta 
Value: false Type: Boolean Description: = true, if the constant parameter value is to be used instead of the input connector 
portA 
Type: FlowPort Description: Flow from/to Stock A 


portB 
Type: FlowPort Description: Flow to/from Stock B 

y_B 
Type: RealOutput_B Description: Rate for flow to and from B (positive value indicates inflow) 

y1_B 
Type: RealOutput_B Description: Rate for flow to and from B (positive value indicates inflow) 

y1_A 
Type: RealOutput_A Description: Rate for flow to and from A (positive value indicates inflow) 

y_A 
Type: RealOutput_A Description: Rate for flow to and from A (positive value indicates inflow) 

dataIn 
Type: InputConnector Description: Inputs for predatorprey model 

u_alpha 
Type: RealOutput Description: Output signal 

u_beta 
Type: RealOutput Description: Output signal 

u_gamma 
Type: RealOutput Description: Output signal 

u_delta 
Type: RealOutput Description: Output signal 

dataBus 
Type: DataBus Description: Expandable connector for multiple data signals (input/output) 
complexInteraction 
Type: ComplexInteraction Description: Combined linear and nonlinear interaction 


zeroRate 
Type: ConstantConverter Description: Zero rate input 

fractionalGrowthRatePredator 
Type: Gain Description: Convert rate of delince to growth rate 

couplingFactorForPrey 
Type: Gain Description: Convert rate of delince to growth rate 

parAlpha 
Type: ConstantConverter Description: Constant alpha (optional) 

parBeta 
Type: ConstantConverter Description: Constant beta (optional) 

parGamma 
Type: ConstantConverter Description: Constant gamma (optional) 

parDelta 
Type: ConstantConverter Description: Constant delta (optional) 
BusinessSimulation.Examples Predatorprey dynamics 
InputConnector
defined as encapsulated expandable connector
in v2.1.0.unspecified
in v2.1.0.TypeA, TypeB
and corresponding reference levels refA, refB
introduced to support unit checking and unit conversions in v2.2.