code simplifications, growth formula, minor rewordings

README.md

@@ -53,7 +53,7 @@ Besides benefits for performance and maintainability, ECS offers great flexibili
 
 ## Model purpose
 
-The purpose of this model is to demonstrate the use of Entity-Component-Systems for individual-based models.
+The purpose of this model is to demonstrate the use of the ECS approach for individual-based models.
 
 ## Entities, state variables and scales
 
@@ -135,7 +135,7 @@ public class IsSearching extends com.artemis.Component {}
 
 **Resources**
 
-> Resources are "things" that exist only once in the model, contrary to entities, and are potentially available for all submodels. Any instance of a Java class can become a resource. However, only one instance of each class is possible.
+> Resources are objects that exist only once in the model, contrary to entities, and are potentially available for all submodels. When using the Artemis-odb, any instance of a Java class can become a resource. However, only one instance of each class is possible.
 
 Grassers live in a two-dimensional world. The world is represented by a grid of grass that grassers can consume.
 
@@ -201,16 +201,16 @@ public class Main {
 
     // ==> Parameters.
 
-    public static void main(String[] args) {
+    public static void main(String[] args) throws InterruptedException {
         var setup = new WorldConfigurationBuilder()
                 .with(new LogisticGrassGrowth(GRASS_GROWTH_RATE))
                 .with(new Metabolism(ENERGY_CONSUMPTION))
                 .with(new Reproduction(REPRODUCTION_PROB))
                 .with(new GrassingBehaviour(GRASS_START_SEARCHING, GRASS_CONSUMPTION))
                 .with(new SearchBehaviour(GRASS_START_GRASSING, RANDOM_WALK_ANGLE, RANDOM_WALK_SPEED))
-                .with(new Graphics(6))
+                .with(new Graphics())
                 .build()
-                .register(new Randomness(System.currentTimeMillis()))
+                .register(new Randomness(0))
                 .register(new Grass(WORLD_WIDTH, WORLD_HEIGHT, 0.8f));
 
         var world = new World(setup);
@@ -219,9 +219,7 @@ public class Main {
 
         for (int i=0; i < 1000000; i++) {
             world.process();
-            try {
-                Thread.sleep(10);
-            } catch(InterruptedException ignored) {}
+            Thread.sleep(10);
         }
     }
 
@@ -263,7 +261,13 @@ Submodels are described in their order of execution.
 
 ### Grass growth
 
-Grass growth is logistic, with a capacity of 1.0.
+Grass growth is logistic. The amount of grass is updated according 
+
+```math
+p_{t+1} = p_t + r p_t \frac{k - p_t}{k}
+```
+
+where $`p_t`$ is the amount in the current step and $`p_{t+1}`$ in the next step. $`r`$ is the growth rate per step and $`k`$ is the capacity. Capacity is always 1.0.
 
 > Since the grassing system does not use any entities, we simply extend `BaseSystem`. However, it requires access to the `Grass` grid, which is "injected" by the ECS through the line `@Wire Grass grass;`.
 > 
@@ -321,7 +325,7 @@ import grassing.comp.Energy;
 @All(Energy.class)
 public class Metabolism extends IteratingSystem {
 
-    ComponentMapper<Energy> mEnergy;
+    ComponentMapper<Energy> energy;
 
     private final float consumption;
 
@@ -331,7 +335,7 @@ public class Metabolism extends IteratingSystem {
 
     @Override
     protected void process(int id) {
-        Energy e = mEnergy.get(id);
+        Energy e = energy.get(id);
         e.value -= consumption;
         if(e.value <= 0) {
             world.delete(id);
@@ -366,8 +370,8 @@ import grassing.res.Randomness;
 @All({Position.class, Energy.class})
 public class Reproduction extends IteratingSystem {
 
-    ComponentMapper<Position> mPosition;
-    ComponentMapper<Energy> mEnergy;
+    ComponentMapper<Position> position;
+    ComponentMapper<Energy> energy;
 
     @Wire Randomness random;
 
@@ -380,8 +384,8 @@ public class Reproduction extends IteratingSystem {
     @Override
     protected void process(int id) {
         if(random.rng.nextFloat() < reproductionProb) {
-            var pos = mPosition.get(id);
-            var e = mEnergy.get(id);
+            var pos = position.get(id);
+            var e = energy.get(id);
             int entity = world.create();
             world.edit(entity)
                     .add(new Position(pos.x, pos.y))
@@ -418,10 +422,10 @@ import grassing.res.Grass;
 @All({Position.class, Energy.class, IsGrassing.class})
 public class GrassingBehaviour extends IteratingSystem {
 
-    ComponentMapper<Position> mPosition;
-    ComponentMapper<Energy> mEnergy;
-    ComponentMapper<IsGrassing> mGrassing;
-    ComponentMapper<IsSearching> mSearching;
+    ComponentMapper<Position> position;
+    ComponentMapper<Energy> energy;
+    ComponentMapper<IsGrassing> grassing;
+    ComponentMapper<IsSearching> searching;
 
     @Wire Grass grass;
 
@@ -435,18 +439,18 @@ public class GrassingBehaviour extends IteratingSystem {
 
     @Override
     protected void process(int id) {
-        Energy e = mEnergy.get(id);
+        Energy e = energy.get(id);
         if(e.value >= 1) {
             return;
         }
-        Position pos = mPosition.get(id);
+        Position pos = position.get(id);
         float g = grass.grass.get((int) pos.x, (int) pos.y);
         if( g - consumption > minGrass ) {
             e.value += consumption;
             grass.grass.set((int) pos.x, (int) pos.y, g - consumption);
         } else {
-            mGrassing.remove(id);
-            mSearching.create(id);
+            grassing.remove(id);
+            searching.create(id);
         }
     }
 }
@@ -476,10 +480,10 @@ import grassing.util.MathUtil;
 @All({Position.class, Heading.class, IsSearching.class})
 public class SearchBehaviour extends IteratingSystem {
 
-    ComponentMapper<Position> mPosition;
-    ComponentMapper<Heading> mHeading;
-    ComponentMapper<IsGrassing> mGrassing;
-    ComponentMapper<IsSearching> mSearching;
+    ComponentMapper<Position> position;
+    ComponentMapper<Heading> heading;
+    ComponentMapper<IsGrassing> grassing;
+    ComponentMapper<IsSearching> searching;
 
     @Wire Grass grass;
     @Wire Randomness random;
@@ -496,29 +500,29 @@ public class SearchBehaviour extends IteratingSystem {
 
     @Override
     protected void process(int id) {
-        Position pos = mPosition.get(id);
+        Position pos = position.get(id);
         float g = grass.grass.get((int) pos.x, (int) pos.y);
         if( g >= minGrass ) {
-            mSearching.remove(id);
-            mGrassing.create(id);
+            searching.remove(id);
+            grassing.create(id);
         } else {
             randomWalk(id);
         }
     }
 
     private void randomWalk(int id) {
-        var pos = mPosition.get(id);
-        var heading = mHeading.get(id);
-        heading.angle += (float) random.rng.nextGaussian() * maxAngle;
+        var pos = position.get(id);
+        var head = heading.get(id);
+        head.angle += (float) random.rng.nextGaussian() * maxAngle;
 
-        var head = MathUtil.heading(heading.angle);
-        float xNew = pos.x + head.x * speed;
-        float yNew = pos.y + head.y * speed;
+        var h = MathUtil.heading(head.angle);
+        float xNew = pos.x + h.x * speed;
+        float yNew = pos.y + h.y * speed;
         if(grass.grass.contains((int) xNew, (int) yNew)) {
             pos.x = xNew;
             pos.y = yNew;
         } else {
-            heading.angle = (heading.angle + (float) Math.PI) % (2 * (float) Math.PI);
+            head.angle = (head.angle + (float) Math.PI) % (2 * (float) Math.PI);
         }
     }
 }
@@ -566,7 +570,7 @@ Grassers have a reproduction probability of 5% per step.
 final static float REPRODUCTION_PROB = 0.05f;
 ```
 
-Grassers walk with 0.25 units per step, and turn with values from a normal distribution with a standard deviation of 30°.
+Grassers walk with 0.25 units per step, and turn with values from a normal distribution with a mean of 0° and a standard deviation of 30°.
 
 ```java
 /// Parameters

md/appendix.md

@@ -35,19 +35,19 @@ import java.awt.*;
 @One({IsGrassing.class, IsSearching.class})
 public class Graphics extends BaseEntitySystem {
 
-    protected ComponentMapper<Position> mPosition;
-    protected ComponentMapper<Heading> mHeading;
-    protected ComponentMapper<IsGrassing> mGrassing;
-    protected ComponentMapper<IsSearching> mSearching;
+    protected ComponentMapper<Position> position;
+    protected ComponentMapper<Heading> heading;
+    protected ComponentMapper<IsGrassing> grassing;
+    protected ComponentMapper<IsSearching> searching;
 
     @Wire Grass grass;
 
-    final private int cellSize;
     private JPanel canvas;
-
-    public Graphics(int cellSize) {
+    
+    final private int CELL_SIZE = 6;
+    
+    public Graphics() {
         super();
-        this.cellSize = cellSize;
     }
 
     @Override
@@ -62,7 +62,7 @@ public class Graphics extends BaseEntitySystem {
             }
         };
 
-        var dim = new Dimension(grass.grass.width * cellSize, grass.grass.height * cellSize);
+        var dim = new Dimension(grass.grass.width * CELL_SIZE, grass.grass.height * CELL_SIZE);
         canvas.setPreferredSize( dim );
 
         frame.add(canvas);
@@ -73,12 +73,12 @@ public class Graphics extends BaseEntitySystem {
 
     @Override
     protected void processSystem() {
-        canvas.paintImmediately(0, 0, grass.grass.width * cellSize, grass.grass.height * cellSize);
+        canvas.paintImmediately(0, 0, grass.grass.width * CELL_SIZE, grass.grass.height * CELL_SIZE);
     }
     
     void paint(Graphics2D g2d) {
         FloatGrid grass = this.grass.grass;
-        int s = cellSize;
+        int s = CELL_SIZE;
 
         g2d.setBackground(Color.BLACK);
 
@@ -94,11 +94,11 @@ public class Graphics extends BaseEntitySystem {
         IntBag grassers = subscription.getEntities();
         for (int i = 0; i < grassers.size(); i++) {
             int entity = grassers.get(i);
-            var pos = mPosition.get(entity);
-            var head = mHeading.get(entity);
-            if(mGrassing.has(entity)) {
+            var pos = position.get(entity);
+            var head = heading.get(entity);
+            if(grassing.has(entity)) {
                 g2d.setPaint(Color.WHITE);
-            } else if(mSearching.has(entity)) {
+            } else if(searching.has(entity)) {
                 g2d.setPaint(Color.ORANGE);
             } else {
                 g2d.setPaint(Color.MAGENTA);