[Minuit2] Remove unused and controversial X_pos and X_neg functions

Remove unused and controversial `X_pos` and `X_neg` functions from the
MnParabola.

Also, reduce the documentation a bit because it was too verbose for what
the class represents.

Author: guitargeek

math/minuit2/inc/Minuit2/MnParabola.h

@@ -30,118 +30,29 @@ and Lorenzo Moneta
 class MnParabola {
 
 public:
-   /**
-
-   Constructor that initializes the parabola with its three parameters.
-
-   @param a the coefficient of the quadratic term
-   @param b the coefficient of the linear term
-   @param c the constant
-
-   */
-
+   /// Constructor that initializes the parabola with its three parameters.
+   ///
+   /// @param a the coefficient of the quadratic term.
+   /// @param b the coefficient of the linear term.
+   /// @param c the constant.
    MnParabola(double a, double b, double c) : fA(a), fB(b), fC(c) {}
 
-   /**
-
-   Evaluates the parabola a the point x.
-
-   @param x the coordinate where the parabola needs to be evaluated.
-
-   @return the y coordinate of the parabola corresponding to x.
-
-   */
-
+   /// Evaluates the parabola a the point x.
    double Y(double x) const { return (fA * x * x + fB * x + fC); }
 
-   /**
-
-   Calculates the bigger of the two x values corresponding to the
-   given y Value.
-
-   <p>
-
-   ???????!!!!!!!!! And when there is none?? it looks like it will
-   crash?? what is sqrt (-1.0) ?
-
-   @param y the y Value for which the x Value is to be calculated.
-
-   @return the bigger one of the two corresponding values.
-
-   */
-
-   // ok, at first glance it does not look like the formula for the quadratic
-   // equation, but it is!  ;-)
-   double X_pos(double y) const { return (std::sqrt(y / fA + Min() * Min() - fC / fA) + Min()); }
-   // maybe it is worth to check the performance improvement with the below formula??
-   //   double X_pos(double y) const {return (std::sqrt(y/fA + fB*fB/(4.*fA*fA) - fC/fA)  - fB/(2.*fA));}
-
-   /**
-
-   Calculates the smaller of the two x values corresponding to the
-   given y Value.
-
-   <p>
-
-   ???????!!!!!!!!! And when there is none?? it looks like it will
-   crash?? what is sqrt (-1.0) ?
-
-   @param y the y Value for which the x Value is to be calculated.
-
-   @return the smaller one of the two corresponding values.
-
-   */
-
-   double X_neg(double y) const { return (-std::sqrt(y / fA + Min() * Min() - fC / fA) + Min()); }
-
-   /**
-
-   Calculates the x coordinate of the Minimum of the parabola.
-
-   @return x coordinate of the Minimum.
-
-   */
-
+   /// Calculate the x coordinate of the Minimum of the parabola.
    double Min() const { return -fB / (2. * fA); }
 
-   /**
-
-   Calculates the y coordinate of the Minimum of the parabola.
-
-   @return y coordinate of the Minimum.
-
-   */
-
+   /// Calculate the y coordinate of the Minimum of the parabola.
    double YMin() const { return (-fB * fB / (4. * fA) + fC); }
 
-   /**
-
-   Accessor to the coefficient of the quadratic term.
-
-   @return the coefficient of the quadratic term.
-
-    */
-
+   /// Get the coefficient of the quadratic term.
    double A() const { return fA; }
 
-   /**
-
-   Accessor to the coefficient of the linear term.
-
-   @return the coefficient of the linear term.
-
-   */
-
+   /// Get the coefficient of the linear term.
    double B() const { return fB; }
 
-   /**
-
-   Accessor to the coefficient of the constant term.
-
-   @return the coefficient of the constant term.
-
-   */
-
+   /// Get the coefficient of the constant term.
    double C() const { return fC; }
 
 private: