8  Particles

Ichthyop particles (Particle.java class) contains the attributes described in Table 8.1.

Table 8.1: Particle state variables

Variable	Description	Type	Units
x	Particle x position within the grid	float, \(\in [0, N_{x} - 1]\)
y	Particle y position within the grid	float, \(\in [0, N_{y} - 1]\)
z	Particle z position within the grid	float, \(\in [0, N_{z} - 1]\)
dx	Particle increment/decrement of x position	float
dy	Particle increment/decrement of y position	float
dz	Particle increment/decrement of z position	float
lat	Particle longitude	float	Degrees East
lon	Particle latitude	float	Degrees North
depth	Particle depth	float, < 0	m
index	Particle index	int, \(\in [0, N_{part} - 1]\)
age	Particle age	int	seconds
deathCause	Mortality status	ParticleMortality
living	True if a particle is alive	bool
locked	True if a particle is locked	bool
layers	List of additional particle layers	List<ParticleLayer>

When using Ichthyop with additional processes, such as growth or DEB processes, additional variables need to be tracked.

This is done by firsr creating a layer class, which should extend the ParticleLayer.java class. An exemple if provided as follows:

package org.previmer.ichthyop.particle;

public class LengthParticleLayer extends ParticleLayer {

   private double length;

   public LengthParticleLayer(IParticle particle) {
      super(particle);
   }

   @Override
   public void init() {
      length = 0;
   }

   public double getLength() {
      return length;
   }

   public void incrementLength(double dlength) {
      length += dlength;
   }
}

This class contains additional particle attributes (here, for instance length) and methods that can return and modify these attributes.

These new variables can be accessed as follows:

LengthParticleLayer lengthLayer = (LengthParticleLayer) particle.getLayer(LengthParticleLayer.class);
lengthLayer.setLength(length_init);

During the first call to the getLayer method applied to a given layer class, the latter will be instanciated, initialized and add to the particle’s layers list attribute, as shown below.

graph TD;

    id1("Call to getLayer()")
    id2{"Already called?"}

    id1-->id2

    id3(Create Layer)
    id4(Init. layer)
    id5(Get layer)

    id2 -->|No| id3
    id3 --> id4
    id4 --> id5

    id2 -->|Yes| id5

Order in which managers are mobilized.