QwtSpline (3)

#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

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;
}

QwtSpline::QwtSpline (const \fBQwtSpline\fP &other)

Copy constructor

Parameters:

other Spline used for initilization

bool QwtSpline::buildNaturalSpline (const QPolygonF &points)\fC [protected]\fP

Determines the coefficients for a natural spline. Returns:

true if successful

bool QwtSpline::buildPeriodicSpline (const QPolygonF &points)\fC [protected]\fP

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

\fBQwtSpline\fP & QwtSpline::operator= (const \fBQwtSpline\fP &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 (\fBSplineType\fPsplineType)

Select the algorithm used for calculating the spline

Parameters:

splineType Spline type

See also:

splineType()

\fBQwtSpline::SplineType\fP 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.

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