main/src/georegression/geometry/UtilVector2D_F64.java
public static Vector2D_F64 minus( Point2D_F64 a , Point2D_F64 b , Vector2D_F64 output ) {
		if( output == null )
			output = new Vector2D_F64();

		output.x = a.x - b.x;
		output.y = a.y - b.y;

		return output;
	}
public static Vector2D_F64 minus( Point2D_F64 a , Point2D_F64 b , Vector2D_F64 output ) {
		if( output == null )
			output = new Vector2D_F64();

		output.x = a.x - b.x;
		output.y = a.y - b.y;

		return output;
	}
Sets the vector equal to 'a' - 'b'.

@param a point
@param b point
@param output (output) optional storage for vector.
@return Solution