NAME

       c_csa1xs - cubic spline approximation, expanded entry for one-dimensional input

FUNCTION PROTOTYPE

       float *c_csa1xs(int, float [], float [], float [], int,
                    float, int, int, float [], int *);

SYNOPSIS

       float *c_csa1xs(int n, float xi[], float yi[], float wts[],
                       int knots, float smth, int nderiv,
                       int m, float xo[], int *ier);

DESCRIPTION

       n           (integer,input)  The  number  of  input data points. It must be that n is greater than 3 and,
                   depending on the size of knots below, n may have to be larger.

       xi          (real, input) An array dimensioned for n containing the abscissae for the input function.

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

       wts         (real, input) An array dimensioned for n containing weights for the yi values at the input xi
                   values,  that is, wts[l] is a weight for the value of yi[l] for l=0,n-1. If you do not desire
                   to weight the input yi values, then set wts[0] to -1.  The  weights  in  the  wts  array  are
                   relative  and may be set to any non-negative value.  When c_csa1xs is called, the weights are
                   summed and the individual weights are normalized so that the weight sum is unity.

       knots       (integer, input) The number of knots to be used in  constructing  the  approximation  spline.
                   knots  must  be at least 4. The larger the value for knots, the closer the approximated curve
                   will come to passing through the input function values.

       smth        (real, input) A parameter that controls extrapolation into data sparse regions.  If  smth  is
                   zero,  then  nothing special is done in data sparse regions.  A good first choice for smth is
                   1.

       nderiv      (integer, input) Specifies whether you want functional values  (nderiv=0),  first  derivative
                   values (nderiv=1), or second derivative values (nderiv=2).

       m           (integer, input) The number of values to be calculated for the output curve.

       xo          (real, input) An array dimensioned for m containing the X coordinates of the output curve.

       ier         (pointer  to integer, output) An error return value. If *ier is returned as 0, then no errors
                   were detected. If *ier is non-zero, then refer to the error  list  in  the  error  table  for
                   details.

USAGE

       c_csa1xs  is  called  to  find an approximating cubic spline for one-dimensional input data.  c_csa1xs is
       called if you want to weight the input data values, calculate derivatives, or handle  data  sparse  areas
       specially.  If you do not want to do any of these three things, then use c_csa1s.

       c_csa1s returns a pointer to a linear array of data that is the approximated curve.

ACCESS

       To use c_csa1xs, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, c_csa1s, c_csa1ls, c_csa1lxs

       Complete documentation for Csagrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html

COPYRIGHT

       Copyright (C) 2000
       University Corporation for Atmospheric Research

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

UNIX                                              January 1999                                  c_csa1xs(3NCARG)