QwtSpline(3)

NAME
QwtSpline -

SYNOPSIS

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:.RS 4
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:.RS 4
#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;
}

Definition at line 77 of file qwt_spline.h.

  Public Types
enum SplineType { Natural, Periodic }

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

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

  Protected Attributes
PrivateData * d_data

Constructor & Destructor Documentation

  QwtSpline::QwtSpline ()
Constructor.
Definition at line 73 of file qwt_spline.cpp.
References d_data.

  QwtSpline::~QwtSpline ()
Destructor.
Definition at line 90 of file qwt_spline.cpp.
References d_data.

Member Function Documentation

  bool QwtSpline::setPoints (const QPolygonF & points)
Determine the function table index corresponding to a value x 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:
    x
    y points
    size number of points
    periodic if true, calculate periodic spline
Returns:
    true if successful
Warning:
    The sequence of x (but not y) values has to be strictly monotone increasing, which means x[0] < x[1] < .... < x[n-1]. If this is not the case, the function will return false
Definition at line 126 of file qwt_spline.cpp.

  QPolygonF QwtSpline::points () const
Return points passed by setPoints
Definition at line 164 of file qwt_spline.cpp.

  void QwtSpline::reset ()
Free allocated memory and set size to 0.
Definition at line 172 of file qwt_spline.cpp.
References d_data.

  bool QwtSpline::isValid () const
True if valid.
Definition at line 181 of file qwt_spline.cpp.
References d_data.

  double QwtSpline::value (double x) const
Calculate the interpolated function value corresponding to a given argument x.
Definition at line 190 of file qwt_spline.cpp.
References d_data.

  bool QwtSpline::buildNaturalSpline (const QPolygonF & points) [protected]
Determines the coefficients for a natural spline.
Returns:
    true if successful
Definition at line 209 of file qwt_spline.cpp.

  bool QwtSpline::buildPeriodicSpline (const QPolygonF & points) [protected]
Determines the coefficients for a periodic spline.
Returns:
    true if successful
Definition at line 292 of file qwt_spline.cpp.

Author
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