public static final BigInteger determinant(BigInteger p_x_1,BigInteger p_y_1,BigInteger p_x_2,BigInteger p_y_2){
  BigInteger tmp1=p_x_1.multiply(p_y_2);
  BigInteger tmp2=p_x_2.multiply(p_y_1);
  return tmp1.subtract(tmp2);
}

public static final BigInteger determinant ( BigInteger p_x_1 , BigInteger p_y_1 , BigInteger p_x_2 , BigInteger p_y_2 ) { BigInteger tmp1 = p_x_1 . multiply ( p_y_2 ) ; BigInteger tmp2 = p_x_2 . multiply ( p_y_1 ) ; return tmp1 . subtract ( tmp2 ) ; }
calculates the determinant of the vectors ( p_x_1 , p_y_1 ) and ( p_x_2 , p_y_2 )
