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QwtSpline(3) Qwt User's Guide QwtSpline(3)

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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Tue Nov 20 2012 Version 5.2.3