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
In order to save storage space, QwtSpline can be advised not to buffer the contents of x and y. This means that the arrays have to remain valid and unchanged for the interpolation to work properly. This can be achieved by calling QwtSpline::copyValues().
Example:.RS 4
#include<qwt_spline.h> #include<iostream.h> QwtSpline s; double x[30], y[30], xInter[300], yInter[300]; int i; for(i=0;i<30;i++) // fill up x[] and y[] cin >> x[i] >> y[i]; if (s.recalc(x,y,30,0) == 0) // build natural spline { for(i=0;i<300;i++) // interpolate { xInter[i] = x[0] + double(i) * (x[29] - x[0]) / 299.0; yInter[i] = s.value( xInter[i] ); } do_something(xInter, yInter, 300); } else cerr << 'Uhhh...;
Definition at line 63 of file qwt_spline.h.
QwtSpline ()
~QwtSpline ()
double value (double x) const
int recalc (double *x, double *y, int n, int periodic=0)
int recalc (const QwtArray< double > &x, const QwtArray< double > &y, int periodic=0)
void copyValues (int tf=1)
CTOR.
Definition at line 31 of file qwt_spline.cpp.
DTOR.
Definition at line 68 of file qwt_spline.cpp.
Advise recalc() to buffer the tabulated function or switch off internal buffering.
By default, QwtSpline maintains an internal copy of the tabulated function given as *x and *y arguments of QwtSpline::recalc().
If QwtSpline::copyValues() is called with zero argument, subsequent calls to QwtSpline::recalc() will not buffer these values anymore and just store the pointers instead. The QwtSpline::value() function will then silently assume that these pointers remained valid and that the contents of the arrays have not been changed since the last QwtSpline::recalc().
If called with no or nonzero argument, any following QwtSpline::recalc() calls will use the internal buffer.
Parameters:
Warning:
Definition at line 61 of file qwt_spline.cpp.
re-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. It also buffers the values of x and y, which are needed for the interpolation (See QwtSpline::value()).
Parameters:
Returns:
Warning:
Definition at line 206 of file qwt_spline.cpp.
re-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. By default, it also buffers the values of x and y, which are needed for the interpolation (See QwtSpline::value()). In order to save memory, this last behaviour may be changed with the QwtSpline::copyValues() function.
Parameters:
Returns:
Warning:
Definition at line 127 of file qwt_spline.cpp.
Referenced by QwtCurve::drawSpline(), and recalc().
Calculate the interpolated function value corresponding to a given argument x. Definition at line 18 of file qwt_spline.cpp.
Referenced by QwtCurve::drawSpline().
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