Übungstest 7

src/Body.java

@@ -37,14 +37,12 @@ public class Body {
      * Hint: see simulation loop in Simulation.java to find out how this is done.
      */
     public Vector gravitationalForce(Body b) {
-        Vector direction = b.massCenter.minus(this.massCenter);
+        Vector direction = b.massCenter.minus(massCenter);
         double distance = direction.length();
-        if (distance == 0) return direction;
-
+        if (distance == 0) return new Vector();
         direction.normalize();
-        double force = Simulation.G * this.mass * b.mass / (distance * distance);
-        direction.mul(force);
-        return direction;
+        double force = Simulation.G * mass * b.mass / (distance * distance);
+        return direction.times(force);
     }
 
     /**

src/Octree.java

@@ -36,10 +36,11 @@ public class Octree {
         }
     }
 
-    public void applyForces(Body[] bodies, Vector[] forces, double t) {
+    public void applyForces(Body[] bodies, double t) {
         if (root == null) return;
+        Vector[] forces = new Vector[bodies.length];
         for (int i = 0; i < bodies.length; i++) {
-            root.addForcesOnBody(bodies[i], forces[i], t);
+            forces[i] = root.getForcesOnBody(bodies[i], t);
         }
         for (int i = 0; i < bodies.length; i++) {
             bodies[i].move(forces[i]);
@@ -50,6 +51,12 @@ public class Octree {
         if (root == null) return;
         root.draw(cd);
     }
+
+    public int getNumberOfBalancedRegions() {
+        if (root == null || !(root instanceof OctreeNode r)) return 0;
+
+        return r.getNumberOfBalancedRegions();
+    }
 }
 
 abstract class OctreeItem {
@@ -67,8 +74,6 @@ abstract class OctreeItem {
 
     abstract protected Vector getForcesOnBody(Body body, double t);
 
-    abstract protected void addForcesOnBody(Body body, Vector force, double t);
-
     abstract protected void draw(CodeDraw cd);
 }
 
@@ -104,24 +109,18 @@ class OctreeNode extends OctreeItem {
 
     @Override
     protected Vector getForcesOnBody(Body body, double t) {
-        Vector v = new Vector();
-        addForcesOnBody(body, v, t);
-        return v;
-    }
-
-    @Override
-    protected void addForcesOnBody(Body body, Vector force, double t) {
-        double r = center.distanceTo(body.massCenter());
+        double r = pseudoBody.massCenter().distanceTo(body.massCenter());
         if (r == 0) {
-            return;
+            return new Vector();
         } else if (size / r < t) {
-            force.add(body.gravitationalForce(pseudoBody));
-            return;
+            return body.gravitationalForce(pseudoBody);
         }
+        Vector force = new Vector();
         for (OctreeItem child : children) {
             if (child == null) continue;
-            child.addForcesOnBody(body, force, t);
+            force.add(child.getForcesOnBody(body, t));
         }
+        return force;
     }
 
     @Override
@@ -156,6 +155,26 @@ class OctreeNode extends OctreeItem {
                 ((octNum & 4) != 0) ? -1 : 1)
                 .times(this.size / 4));
     }
+
+    private boolean isBalanced() {
+        for (OctreeItem i : children) {
+            if (!(i instanceof OctreeLeaf))
+                return false;
+        }
+        return true;
+    }
+
+    protected int getNumberOfBalancedRegions() {
+        if (isBalanced()) return 1;
+
+        int c = 0;
+        for (OctreeItem i : children) {
+            if (i instanceof OctreeNode n) {
+                c += n.getNumberOfBalancedRegions();
+            }
+        }
+        return c;
+    }
 }
 
 class OctreeLeaf extends OctreeItem {
@@ -164,7 +183,7 @@ class OctreeLeaf extends OctreeItem {
     public OctreeLeaf(Vector center, double size, Body body) {
         super(center, size);
         this.body = body;
-        //this.pseudoBody = new Body(this.body);
+        this.pseudoBody = new Body(this.body);
     }
 
     @Override
@@ -174,21 +193,14 @@ class OctreeLeaf extends OctreeItem {
 
     @Override
     protected Vector getForcesOnBody(Body body, double t) {
-        return body.gravitationalForce(body);
-    }
-
-    @Override
-    protected void addForcesOnBody(Body body, Vector force, double t) {
-        force.add(getForcesOnBody(body, t));
+        return body.gravitationalForce(pseudoBody);
     }
 
     @Override
     protected void draw(CodeDraw cd) {
-        /*
         Vector p1 = center.minus(new Vector(size / 2));
         Vector p2 = new Vector(size).minus(new Vector(Simulation.SECTION_SIZE / 2));
         cd.setColor(Color.GREEN);
         cd.drawRectangle(p1.getScreenX(cd), p1.getScreenY(cd), p2.getScreenX(cd), p2.getScreenY(cd));
-         */
     }
 }

src/Simulation.java

@@ -23,7 +23,7 @@ public class Simulation {
     // set some system parameters
     public static final double SECTION_SIZE = 2 * AU; // the size of the square region in space
     public static final int NUMBER_OF_BODIES = 10000;
-    public static final double OVERALL_SYSTEM_MASS = 20 * SUN_MASS; // kilograms
+    public static final double OVERALL_SYSTEM_MASS = 2000 * SUN_MASS; // kilograms
 
     public static void main(String[] args) {
         CodeDraw cd = new CodeDraw();
@@ -48,34 +48,15 @@ public class Simulation {
         }
 
         long seconds = 0;
-        Vector[] forces = new Vector[bodies.length];
-        for (int i = 0; i < forces.length; i++) forces[i] = new Vector();
-
         while (true) {
             seconds++;
 
-            /*
-            BodyLinkedList mergedBodies = new BodyLinkedList();
-            for (Body b1 : bodies) {
-                BodyLinkedList colliding = bodies.removeCollidingWith(b1);
-                for (Body b2 : colliding) {
-                    b1 = b1.merge(b2);
-                }
-                mergedBodies.addLast(b1);
-            }
-            bodies = mergedBodies;
-            */
-            //long n1 = System.nanoTime();
             Octree octree = new Octree(new Vector(0, 0, 0), SECTION_SIZE);
             for (Body body : bodies) {
                 octree.add(body);
             }
-            //long n2 = System.nanoTime();
-            for (Vector f : forces) f.reset();
-            octree.applyForces(bodies, forces, 1);
-            //long n3 = System.nanoTime();
-
-            //System.out.format("%8.3f µs, %8.3f µs\n", (n2 - n1) / 1000.0, (n3 - n2) / 1000.0);
+            System.out.println(octree.getNumberOfBalancedRegions());
+            octree.applyForces(bodies, 100);
 
             if ((seconds % 60) == 0) {
                 cd.clear(Color.BLACK);

src/Vector.java

@@ -58,18 +58,6 @@ public class Vector {
         return new Vector(x * d, y * d, z * d);
     }
 
-    public void mul(double d) {
-        this.x *= d;
-        this.y *= d;
-        this.z *= d;
-    }
-
-    public void div(double d) {
-        this.x /= d;
-        this.y /= d;
-        this.z /= d;
-    }
-
     /**
      * Returns the sum of this vector and -1*v.
      */
@@ -92,7 +80,7 @@ public class Vector {
      * Returns the length (norm) of this vector.
      */
     public double length() {
-        return Math.sqrt(x * x + y * y + z * z);
+        return distanceTo(new Vector());
     }
 
     /**
@@ -100,13 +88,10 @@ public class Vector {
      * The direction and orientation of the vector is not affected.
      */
     public void normalize() {
-        div(length());
-    }
-
-    public void reset() {
-        x = 0;
-        y = 0;
-        z = 0;
+        double length = length();
+        x /= length;
+        y /= length;
+        z /= length;
     }
 
     public double getScreenX(CodeDraw cd) {