//*********************************************************************************
// class tig.maths.Vector2
// Software released under the General Public License (version 2 or later), available at
// http://www.gnu.org/copyleft/gpl.html
//*********************************************************************************

package tig.maths;
/**********************************************************************************
Simple representation of a vector in a 2D space.

Represented as 2 doubles.
@author Thierry Graff
@history apr 29 2002 : creation from Vector3
**********************************************************************************/
public class Vector2{

  //=================================================================================
  //                            CONSTANTS
  //=================================================================================
  /** First coordinate of this vector. */
  public double x0;
  /** Second coordinate of this vector. */
  public double x1;
					 
  //=================================================================================
  //                            CONSTRUCTORS
  //=================================================================================
  /** Constructor from 2 doubles. */
  public Vector2(double a0, double a1){
    x0 = a0; x1 = a1;
  }// end Vector2

  /** Constructor from an array containing 2 doubles.
  @throws IllegalArgumentException if coords.length != 2.
  */
  public Vector2(double[] coords){
    if (coords.length != 2)
      throw new IllegalArgumentException("Array passed to Vector2 constructor "
                                       + "must have 2 elements");
    x0 = coords[0]; x1 = coords[1];
  }// end Vector2

  //=================================================================================
  //                            PUBLIC METHODS
  //=================================================================================

  /** Returns a String representation of this Vector. The form is : (x0, x1). */
  public String toString(){
    return "(" + this.x0 + ", " + this.x1 + ")";
  }// end toString()

  //=================================================================================
  //                            STATIC METHODS
  //=================================================================================

  /** Returns the norm of the vector passed in parameter. */
  public static double norm(Vector2 v){
    return Math.sqrt(v.x0*v.x0 + v.x1*v.x1);
  }// end norm()

  /** Multiplication of a vector by a matrix ; returns a vector b such as b = M a. */
  public static Vector2 mul(Matrix2 M, Vector2 a){
    return new Vector2(M.m00*a.x0 + M.m01*a.x1,
                        M.m10*a.x0 + M.m11*a.x1);
  }// end mul(Matrix2, Vector2)

  /** Multiplication of a vector by a scalar ; returns a vector b such as b = k a. */
  public static Vector2 mul(double k, Vector2 a){
    return new Vector2(k*a.x0, k*a.x1);
  }// end mul(double, Vector2)
  
  /** Returns a Vector2 c such as c = a - b. */
  public static Vector2 sub(Vector2 a, Vector2 b){
    return new Vector2(a.x0 - b.x0, a.x1 - b.x1);
  }// end sub
  
  /** Returns a Vector2 c such as c = a + b. */
  public static Vector2 add(Vector2 a, Vector2 b){
    return new Vector2(a.x0 + b.x0, a.x1 + b.x1);
  }// end add
  
  /** Returns a Vector2 b such as b = -a. */
  public static Vector2 negate(Vector2 a){
    return new Vector2(-a.x0, -a.x1);
  }// end negate
  
}//end class Vector2