QwtSpline(3)

NAME
QwtSpline - A class for spline interpolation.

SYNOPSIS

#include <qwt_spline.h>

  Public Types

enum SplineType { Natural, Periodic }
Spline type.

  Public Member Functions

QwtSpline ()
Constructor.
QwtSpline (const QwtSpline &)
~QwtSpline ()
Destructor.
QwtSpline & operator= (const QwtSpline &)
void setSplineType (SplineType)
SplineType splineType () const
bool setPoints (const QPolygonF &points)
Calculate the spline coefficients.
QPolygonF points () const
void reset ()
Free allocated memory and set size to 0.
bool isValid () const
True if valid.
double value (double x) const
const QVector< double > & coefficientsA () const
const QVector< double > & coefficientsB () const
const QVector< double > & coefficientsC () const

  Protected Member Functions

bool buildNaturalSpline (const QPolygonF &)
Determines the coefficients for a natural spline.
bool buildPeriodicSpline (const QPolygonF &)
Determines the coefficients for a periodic spline.

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;
    }

Member Enumeration Documentation

  enum QwtSpline::SplineType

Spline type.
Enumerator
Natural
    A natural spline.
Periodic
    A periodic spline.

Constructor & Destructor Documentation

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

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 QVector< double > & QwtSpline::coefficientsA () const

Returns:
    A coefficients

  const QVector< double > & QwtSpline::coefficientsB () const

Returns:
    B coefficients

  const QVector< double > & QwtSpline::coefficientsC () const

Returns:
    C coefficients

  QwtSpline & QwtSpline::operator= (const QwtSpline & other)
Assignment operator
Parameters:
    other Spline used for initialization
Returns:
    *this

  QPolygonF QwtSpline::points () const

Returns:
    Points, that have been 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 (SplineType splineType)
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 (double x) const
Calculate the interpolated function value corresponding to a given argument x.
Parameters:
    x Coordinate
Returns:
    Interpolated coordinate

Author
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