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.