Simple model of animal movement

Model : hunter1
Simile version : 3.1+
Date added : 2003-06-20
Keywords : Movement ; Individual-based ; Spatial modelling ; Fixed-membership submodel ; System Dynamics ;

Description

This models the partly-random movement of an animal on a plane surface.

We use three state variables: one for the animal’s x-coordinate, one for its y coordinate, and one for the direction it is currently facing.

Each time step, the animal changes its direction slightly to the left or right (by selecting a change-of-direction value randomly from a range of angles), then moves ahead that amount. We need a bit of trigonometry to work out how much the x and y values change knowing the new direction and the distance it travels each time step (i.e. its speed).

The model includes an edge detector, to stop the animal wandering off the screen.

Files

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hunter1.sml

Diagram

Equations

Equations in PREDATOR
Compartments:
  X:   initial value=rand(30,70)
  Dir: initial value=rand(0,6.28)
  Y:   initial value==rand(30,70)

Flows:
  xchange   = (if outside==1 then speed*cos(dir+3.14)else speed*cos(dir))
  dirchange = (if outside==1 then 3.14/dt(1)else rand(-0.4,0.4)/dt(1))
  ychange   = (if outside==1 then speed*sin(dir+3.14)else speed*sin(dir))

Variables:
  speed     = 5
  size      = 3
  outside   = (if (x<0;x>100;y<0;y>100)then 1 else 0)

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