qwtspline.3

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.TH "QwtSpline" 3 "4 Nov 2003" "Qwt User's Guide" \" -*- nroff -*-
.ad l
.nh
.SH NAME
QwtSpline \- 
.SH SYNOPSIS
.br
.PP
.SH "Detailed Description"
.PP 
A class for spline interpolation. 

The QwtSpline class is used for cubical spline interpolation. Two types of splines, natural and periodic, are supported.
.PP
\fBUsage:\fP.RS 4

.IP "1." 4
First call \fBQwtSpline::recalc()\fP to determine the spline coefficients for a tabulated function y(x). 
.IP "2." 4
After the coefficients have been set up, the interpolated function value for an argument x can be determined by calling \fBQwtSpline::value()\fP. 
.PP
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 \fBQwtSpline::copyValues()\fP.
.RE
.PP
\fBExample:\fP.RS 4

.PP
.nf
#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...\n';

.PP
.RE
.PP

.PP
.SS "Public Member Functions"

.in +1c
.ti -1c
.RI "\fBQwtSpline\fP ()"
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.ti -1c
.RI "\fB~QwtSpline\fP ()"
.br
.ti -1c
.RI "double \fBvalue\fP (double x) const "
.br
.ti -1c
.RI "int \fBrecalc\fP (double *x, double *y, int n, int periodic=0)"
.br
.ti -1c
.RI "int \fBrecalc\fP (const  QwtArray< double > &x, const  QwtArray< double > &y, int periodic=0)"
.br
.ti -1c
.RI "void \fBcopyValues\fP (int tf=1)"
.br
.in -1c
.SH "Constructor & Destructor Documentation"
.PP 
.SS "QwtSpline::QwtSpline ()"
.PP
CTOR. 
.SS "QwtSpline::~\fBQwtSpline\fP ()"
.PP
DTOR. 
.SH "Member Function Documentation"
.PP 
.SS "void QwtSpline::copyValues (int tf = 1)"
.PP
Advise \fBrecalc()\fP 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 \fBQwtSpline::recalc()\fP.
.PP
If \fBQwtSpline::copyValues()\fP is called with zero argument, subsequent calls to \fBQwtSpline::recalc()\fP will not buffer these values anymore and just store the pointers instead. The \fBQwtSpline::value()\fP function will then silently assume that these pointers remained valid and that the contents of the arrays have not been changed since the last \fBQwtSpline::recalc()\fP.
.PP
If called with no or nonzero argument, any following \fBQwtSpline::recalc()\fP calls will use the internal buffer.
.PP
\fBParameters:\fP
.RS 4
\fItf\fP if nonzero, the function table will be buffered 
.RE
.PP
\fBWarning:\fP
.RS 4
\fBcopyValues()\fP resets all the contents of QwtSpline. A subsequent \fBrecalc()\fP will be necessary. 
.RE
.PP

.SS "int QwtSpline::recalc (const QwtArray< double > & x, const QwtArray< double > & y, int periodic = 0)"
.PP
re-calculate the spline coefficients Depending on the value of \fIperiodic\fP, 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 \fBQwtSpline::value()\fP). 
.PP
\fBParameters:\fP
.RS 4
\fIx\fP QwtArray<double> of points 
.br
\fIy\fP QwtArray<double> of points 
.br
\fIperiodic\fP if non-zero, calculate periodic spline 
.RE
.PP
\fBReturns:\fP
.RS 4
.IP "\fB0\fP" 1c
successful 
.IP "\fBQwt::ErrMono<dd>Sequence of x values is not strictly monotone increasing \fP" 1c
.IP "\fBQwt::ErrNoMem<dd>Couldn't allocate memory \fP" 1c
.PP
.RE
.PP
\fBWarning:\fP
.RS 4
The sequence of x (but not y) values has to be strictly monotone increasing, which means \fCx[0] < x[1] < .... < x[n-1]\fP. If this is not the case, the function will return an error. 
.RE
.PP

.SS "int QwtSpline::recalc (double * x, double * y, int n, int periodic = 0)"
.PP
re-calculate the spline coefficients Depending on the value of \fIperiodic\fP, 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 \fBQwtSpline::value()\fP). In order to save memory, this last behaviour may be changed with the \fBQwtSpline::copyValues()\fP function.
.PP
\fBParameters:\fP
.RS 4
\fIx\fP .br
\fIy\fP points 
.br
\fIn\fP number of points 
.br
\fIperiodic\fP if non-zero, calculate periodic spline 
.RE
.PP
\fBReturns:\fP
.RS 4
.IP "\fB0\fP" 1c
successful 
.IP "\fBQwt::ErrMono<dd>Sequence of x values is not strictly monotone increasing \fP" 1c
.IP "\fBQwt::ErrNoMem<dd>Couldn't allocate memory \fP" 1c
.PP
.RE
.PP
\fBWarning:\fP
.RS 4
The sequence of x (but not y) values has to be strictly monotone increasing, which means \fCx[0] < x[1] < .... < x[n-1]\fP. If this is not the case, the function will return an error. 
.RE
.PP

.SS "double QwtSpline::value (double x) const"
.PP
Calculate the interpolated function value corresponding to a given argument x. 

.SH "Author"
.PP 
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