bionic (3) c_ftcurvps.3NCARG.gz

NAME

       c_ftcurvps - compute a smoothing spline for periodic functions.

FUNCTION PROTOTYPE

       int c_ftcurvps (int, float [], float [], float, int, float [], int,
                         float [], float []);

SYNOPSIS

       int c_ftcurvps (n, xi, yi, p, dflg, d, m, xo, yo);

DESCRIPTION

       n           The number of input data points. (n > 1)

       xi          An array containing the abscissae for the input function.

       yi          An  array  containing  the  functional  values of the input function (yi[k] is the functional
                   value at x[k] for k=0,n-1).

       p           The period of the function.

       dflg        A switch for interpreting the value of d (as described below).  If dflg=0, then d is an array
                   of length n (an error estimate for each input data value); if dflg=1, then d is a scalar that
                   serves as an error estimate for every single data item.

       d           A user-specified value containing the observed weights. d may either be an array or a scalar,
                   depending on the value of dflg.

       m           The number of output values.

       xo          Contains the abscissae for the output values.

       yo          Contains  the  functional  values for the smoothing spline ((yo[k] is the functional value at
                   xo[k] for k=0,n-1).

RETURN VALUE

       c_ftcurvps returns an error value as per:

       = 1 if n is less than 2.
       = 2 if smt is negative.
       = 3 if eps is negative or greater than 1.
       = 4 if x values are not strictly increasing.
       = 5 if d is negative.
       = 6 if p is less than or equal to X(N)-X(1).

USAGE

       This function computes an interpolatory smoothing spline under tension through a sequence  of  functional
       values of a periodic function.

       Two  parameters  and one function argument used to control the degree of smoothness -- the parameters are
       smt, and eps and the function argument is d.

       The argument d is a value indicating the degree of confidence in  the  accuracy  of  the  input  function
       values  --  it  should be an approximation of the standard deviation of error. Effectively the value of d
       controls how close the smoothed curve comes  to  the  input  data  points.   If  d  is  small,  then  the
       interpolated  curve  will  pass  close to the input data. The larger the value of d, the more freedom the
       smooth curve has in how close it comes to the input data values.

       The parameter smt is a more subtle global smoothing parameter; smt must be non-negative. For small values
       of  smt, the curve approximates the tension spline and for larger values of smt, the curve is smoother. A
       reasonable value for smt is (float) n.

       The parameter eps controls the precision to which smt is interpreted; eps  must  be  between  0.  and  1.
       inclusive. A reasonable value for eps sqrt( 2./(float) n ).

       c_ftcurvps  is  called  after  all  of  the desired values for control parameters have been set using the
       procedures c_ftseti, c_ftsetr, c_ftsetc. Control parameters that apply to c_ftcurvps are: sig, smt,  eps,
       sf2.

       The value for the parameter sig specifies the tension factor.  Values near zero result in a cubic spline;
       large values (e.g. 50) result in nearly a polygonal line. A typical value is 1. (the default).

ACCESS

       To use c_ftcurvps, load the NCAR Graphics library ngmath.

SEE ALSO

       fitgrid_params, c_ftseti, c_ftsetr, c_ftsetc.

       Complete documentation for Fitgrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/fitgrid/fithome.html

COPYRIGHT

       Copyright (C) 2000
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.