NAME

       c_csa2lxs - cubic spline approximation, expanded entry for two-dimensional input, list output

FUNCTION PROTOTYPE

       float *c_csa2lxs(int, float [], float [], float [], float [], int [],
                        float, int [], int, float [], float [], int *);

SYNOPSIS

       int c_csa2lxs(int n, float xi[], float yi[], float zi[],
                     float wts[], int knots[2], float smth, int nderiv[2],
                     int no, float xo[], float yo[], 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 X coordinate  values  for  the  input
                   function.

       yi          (real,  input)  An  array  dimensioned for n containing the Y coordinate values for the input
                   function.

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

       wts         (real, input) An array containing weights for the zi values at the input xi  and  yi  values,
                   that  is,  wts[l]  is  a  weight  for the value of zi[l] for l=0,n-1. If you do not desire to
                   weight the input zi 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_csa2lxs 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[0]  and  knots[1]  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)  For  each  of  the  two  coordinate  direction, specifies whether you want
                   functional values (nderiv=0), first derivative values (nderiv=1), or second derivative values
                   (nderiv=2). For example, if nderiv[0]=1 and nderiv[1]=1, then the second order mixed  partial
                   would be computed.

       no          (integer, input) The number of X - Y coordinate values to be calculated for the output array.

       xo          (real, input) An array dimensioned for no containing the X coordinates of the output list.

       yo          (real, output) An array dimensioned for no containing the Y coordinates of the output list.

       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_csa2lxs is called to find  values  of  an  approximating  cubic  spline  at  specified  two-dimensional
       coordinates.  If  you  want to weight the input data values, calculate derivatives, or handle data sparse
       areas specially, then you will need to use c_csa2lxs.

       c_csa2lxs returns a pointer to a linear array of data that contains the approximated values calculated at
       the input list of coordinate values. That is, if out is declared as

         float *out;

       and we set:

         out = c_csa2lxs(n, x, y, z, wts, knots, smth, nderiv, no, xo, yo, &ier);

       then out[i] is the approximated function value at coordinate point (xo[i], yo[i]) for 0 <= i  <  no.  The
       space for out is allocated internal to c_csa2lxs and is no floats in size.

ACCESS

       To use c_csa2lxs, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, c_csa2s, c_csa2xs, c_csa2ls

       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_csa2lxs(3NCARG)