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 QwtSpline::recalc() 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().
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>
{
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...0;
Public Member Functions
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)
Constructor & Destructor Documentation
QwtSpline::QwtSpline ()
CTOR.
Definition at line 31 of file qwt_spline.cpp.
QwtSpline::~QwtSpline ()
DTOR.
Definition at line 68 of file qwt_spline.cpp.
Member Function Documentation
void QwtSpline::copyValues (int tf = 1)
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:
tf if nonzero, the function table will be buffered
Warning:
copyValues() resets all the contents of QwtSpline. A subsequent
recalc() will be necessary.
Definition at line 61 of file qwt_spline.cpp.
int QwtSpline::recalc (const QwtArray< double > & x, const QwtArray< double
> & y, int periodic = 0)
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:
x QwtArray<double> of points
y QwtArray<double> of points
periodic if non-zero, calculate periodic spline
Returns:
0 successful
Qwt::ErrMono<dd>Sequence of x values is not strictly monotone
increasing
Qwt::ErrNoMem<dd>Couldn’t allocate memory
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 an error.
Definition at line 206 of file qwt_spline.cpp.
References recalc().
int QwtSpline::recalc (double * x, double * y, int n, int periodic = 0)
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:
x .br y points
n number of points
periodic if non-zero, calculate periodic spline
Returns:
0 successful
Qwt::ErrMono<dd>Sequence of x values is not strictly monotone
increasing
Qwt::ErrNoMem<dd>Couldn’t allocate memory
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 an error.
Definition at line 127 of file qwt_spline.cpp.
Referenced by QwtCurve::drawSpline(), and recalc().
double QwtSpline::value (double x) const
Calculate the interpolated function value corresponding to a given
argument x. Definition at line 18 of file qwt_spline.cpp.
Referenced by QwtCurve::drawSpline().
Author
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