Interaction - Predation

The Modelica By Example target code is:

within ModelicaByExample.Components.LotkaVolterra.Interfaces;
partial model Interaction "Used to describe interactions between two species"
  Species a "Species A"
    annotation ...
  Species b "Species B"
    annotation ...
protected
  Real a_growth "Growth in population of species A (if positive)";
  Real a_decline "Decline in population of species A (if positive)";
  Real b_growth "Growth in population of species B (if positive)";
  Real b_decline "Decline in population of species B (if positive)";
equation
  a_decline = -a_growth;
  a.rate = a_decline;
  b_decline = -b_growth;
  b.rate = b_decline;
end Interaction;

within ModelicaByExample.Components.LotkaVolterra.Components;
model Predation "Model of predation"
  extends Interfaces.Interaction;
  parameter Real beta "Prey (Species A) consumed";
  parameter Real delta "Predators (Species B) fed";
equation
  b_growth = delta*a.population*b.population;
  a_decline = beta*a.population*b.population;
end Predation;

The exported Modelica code for Interaction is:

model Interaction
  Interaction _Interaction;
  model Interaction
    SpeciesFlowElement a;
    SpeciesFlowElement b;
    Rate a_growth;
    Rate a_decline;
    Rate b_growth;
    Rate b_decline;
  equation
    a_decline=-a_growth;
    a.r=a_decline;
    b_decline=-b_growth;
    b.r=b_decline;
  end Interaction;
  connector SpeciesFlowElement
    Population p;
    flow Rate r;
  end SpeciesFlowElement;
  type Rate=Real(unit="1/s");
  type Population=Real;
end Interaction;

The exported Modelica code for Predation is:

model Predation
  Predation _Predation;
  model Predation
    extends Interaction;
    parameter Rate beta;
    parameter Rate delta;
  equation
    b_growth=delta*a.p*b.p;
    a_decline=beta*a.p*b.p;
  end Predation;
  model Interaction
    SpeciesFlowElement a;
    SpeciesFlowElement b;
    Rate a_growth;
    Rate a_decline;
    Rate b_growth;
    Rate b_decline;
  equation
    a_decline=-a_growth;
    a.r=a_decline;
    b_decline=-b_growth;
    b.r=b_decline;
  end Interaction;
  type Rate=Real(unit="1/s");
  connector SpeciesFlowElement
    Population p;
    flow Rate r;
  end SpeciesFlowElement;
  type Population=Real;
end Predation;