Updated double versions.

src/main/java/pythagoras/d/AbstractVector.java

@@ -17,6 +17,17 @@ public abstract class AbstractVector implements IVector
         return x()*other.x() + y()*other.y();
     }
 
+    @Override // from interface IVector
+    public Vector cross (IVector other) {
+        return cross(other, new Vector());
+    }
+
+    @Override // from interface IVector
+    public Vector cross (IVector other, Vector result) {
+        double x = x(), y = y(), ox = other.x(), oy = other.y();
+        return result.set(y*ox - x*oy, x*oy - y*ox);
+    }
+
     @Override // from interface IVector
     public Vector negate () {
         return negate(new Vector());
@@ -125,6 +136,16 @@ public abstract class AbstractVector implements IVector
         return result.set(x() + x, y() + y);
     }
 
+    @Override // from interface IVector
+    public Vector subtract (double x, double y) {
+        return subtract(x, y, new Vector());
+    }
+
+    @Override // from interface IVector
+    public Vector subtract (double x, double y, Vector result) {
+        return result.set(x() - x, y() - y);
+    }
+
     @Override // from interface IVector
     public Vector addScaled (IVector other, double v) {
         return addScaled(other, v, new Vector());

src/main/java/pythagoras/d/IVector.java

@@ -18,6 +18,15 @@ public interface IVector
     /** Computes and returns the dot product of this and the specified other vector. */
     double dot (IVector other);
 
+    /** Computes the cross product of this and the specified other vector.
+     * @return a new vector containing the result. */
+    Vector cross (IVector other);
+
+    /** Computes the cross product of this and the specified other vector, placing the result in
+     * the object supplied.
+     * @return a reference to the result, for chaining. */
+    Vector cross (IVector other, Vector result);
+
     /** Negates this vector.
      * @return a new vector containing the result. */
     Vector negate ();
@@ -106,6 +115,14 @@ public interface IVector
      * @return a reference to the result, for chaining. */
     Vector subtract (IVector other, Vector result);
 
+    /** Subtracts a vector from this one.
+     * @return a new vector containing the result. */
+    Vector subtract (double x, double y);
+
+    /** Subtracts a vector from this one and places the result in the supplied object.
+     * @return a reference to the result, for chaining. */
+    Vector subtract (double x, double y, Vector result);
+
     /** Rotates this vector by the specified angle.
      * @return a new vector containing the result. */
     Vector rotate (double angle);

src/main/java/pythagoras/d/Vector.java

@@ -29,6 +29,13 @@ public class Vector extends AbstractVector
     public Vector () {
     }
 
+    /** Computes the cross product of this and the specified other vector, storing the result in
+     * this vector.
+     * @return a reference to this vector, for chaining. */
+    public Vector crossLocal (IVector other) {
+        return cross(other, this);
+    }
+
     /** Negates this vector in-place.
      * @return a reference to this vector, for chaining. */
     public Vector negateLocal () {