NAME

       QwtSpline -

SYNOPSIS

       #include <qwt_spline.h>

   Public Types
       enum SplineType { Natural, Periodic }

   Public Member Functions
       QwtSpline ()
       QwtSpline (const QwtSpline &)
       ~QwtSpline ()
       const QwtArray< double > & coefficientsA () const
       const QwtArray< double > & coefficientsB () const
       const QwtArray< double > & coefficientsC () const
       bool isValid () const
       QwtSpline & operator= (const QwtSpline &)
       QPolygonF points () const
       void reset ()
       bool setPoints (const QPolygonF &points)
       void setSplineType (SplineType)
       SplineType splineType () const
       double value (double x) const

   Protected Member Functions
       bool buildNaturalSpline (const QPolygonF &)
       bool buildPeriodicSpline (const QPolygonF &)

   Protected Attributes
       PrivateData * d_data

Detailed Description

       A class for spline interpolation.

       The QwtSpline class is used for cubical spline interpolation. Two types of splines,
       natural and periodic, are supported.

       Usage:

           1.  First call setPoints() to determine the spline coefficients for a tabulated
               function y(x).
           2.  After the coefficients have been set up, the interpolated function value for an
               argument x can be determined by calling QwtSpline::value().
       Example:

           #include <qwt_spline.h>

           QPolygonF interpolate(const QPolygonF& points, int numValues)
           {
               QwtSpline spline;
               if ( !spline.setPoints(points) )
                   return points;

               QPolygonF interpolatedPoints(numValues);

               const double delta =
                   (points[numPoints - 1].x() - points[0].x()) / (points.size() - 1);
               for(i = 0; i < points.size(); i++)  / interpolate
               {
                   const double x = points[0].x() + i * delta;
                   interpolatedPoints[i].setX(x);
                   interpolatedPoints[i].setY(spline.value(x));
               }
               return interpolatedPoints;
           }

Constructor & Destructor Documentation

   QwtSpline::QwtSpline (const QwtSpline &other)
       Copy constructor
       Parameters:
           other Spline used for initilization

Member Function Documentation

   bool QwtSpline::buildNaturalSpline (const QPolygonF &points) [protected]
       Determines the coefficients for a natural spline. Returns:
           true if successful
   bool QwtSpline::buildPeriodicSpline (const QPolygonF &points) [protected]
       Determines the coefficients for a periodic spline. Returns:
           true if successful
   const QwtArray< double > & QwtSpline::coefficientsA () const
       Returns:
           A coefficients
   const QwtArray< double > & QwtSpline::coefficientsB () const
       Returns:
           B coefficients
   const QwtArray< double > & QwtSpline::coefficientsC () const
       Returns:
           C coefficients
   QwtSpline & QwtSpline::operator= (const QwtSpline &other)
       Assignment operator
       Parameters:
           other Spline used for initilization
   QPolygonF QwtSpline::points () const
       Return points passed by setPoints
   bool QwtSpline::setPoints (const QPolygonF &points)
       Calculate the spline coefficients. Depending on the value of periodic, this function will
       determine the coefficients for a natural or a periodic spline and store them internally.
       Parameters:
           points Points
       Returns:
           true if successful
       Warning:
           The sequence of x (but not y) values has to be strictly monotone increasing, which
           means points[i].x() < points[i+1].x(). If this is not the case, the function will
           return false
   void QwtSpline::setSplineType (SplineTypesplineType)
       Select the algorithm used for calculating the spline
       Parameters:
           splineType Spline type
       See also:
           splineType()
   QwtSpline::SplineType QwtSpline::splineType () const
       Returns:
           the spline type
       See also:
           setSplineType()
   double QwtSpline::value (doublex) const
       Calculate the interpolated function value corresponding to a given argument x.

Author

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