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.