/**
   This class represents and ordered pair (e,de/dx). e is the value of
   an expression at a particular point, and de/dx is the value of the 
   derivative of that expression evaluated at the same point as the expression.
   Author: Charlie McDowell
 */
class ExprDeriv {
  private double exprValue;
  private double derivValue;
  /**
     Construct an (e, de/dx) object.
   */
  ExprDeriv(double expr, double deriv) {
    exprValue = expr;
    derivValue = deriv;
  }
  /**
     The standard string representation.
     @return This ExprDeriv as a string.
   */
  public String toString() {
    return "(" + exprValue + ", " + derivValue + ")";
  }
  /**
     Perform an addition.
     @param other The right operand of the +.
     @return A new ExprDeriv representing this + other.
   */
  ExprDeriv add(ExprDeriv other) {
    return new ExprDeriv(exprValue + other.exprValue,
			 derivValue + other.derivValue);
  }
  /**
     Perform a subtraction.
     @param other The right operand of the -.
     @return A new ExprDeriv representing this - other.
   */
  ExprDeriv sub(ExprDeriv other) {
    return new ExprDeriv(exprValue - other.exprValue,
			 derivValue - other.derivValue);
  }
  /**
     Perform a multiplication.
     @param other The right operand of the *.
     @return A new ExprDeriv representing this * other.
   */
  ExprDeriv times(ExprDeriv other) {
    return new ExprDeriv(exprValue * other.exprValue,
			 derivValue*other.exprValue + 
			 other.derivValue*exprValue);
  }
  /**
     Perform a division.
     @param other The right operand of the /.
     @return A new ExprDeriv representing this / other.
   */
  ExprDeriv divide(ExprDeriv other) {
    if (exprValue == 0 && other.exprValue == 0)
      return new ExprDeriv(derivValue / other.derivValue, 0);
    else
      {
	ExprDeriv temp =  new ExprDeriv(exprValue / other.exprValue,
			   (derivValue * other.exprValue -
                            exprValue * other.derivValue) /
			   (other.exprValue*other.exprValue));
	return temp;
      }
  }
}