NAME

       c_csa2xs  -  cubic spline approximation, expanded entry for two-dimensional input, gridded
       output

FUNCTION PROTOTYPE

       float *c_csa2xs(int, float [], float [], float [], float [], int [], float,
                       int [], int, int, float [], float [], int *);

SYNOPSIS

       int c_csa2xs(int ni, float xi[], float yi[], float zi[], float wts[],
                    int knots[2], float smth, int nderiv[2], int no, int mo,
                    float xo[], float yo[], int *ier);

DESCRIPTION

       ni          (integer,input) The number of input data points. It must be that ni 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 ni containing the X coordinate values
                   for the input function.

       yi          (real, input) An array dimensioned for ni 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,ni-1.

       wts         (real, input) An array containing weights for the zi values at  the  input  xi
                   values,  that  is,  wts[l] is a weight for the value of zi[l] for l=0,ni-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_csa2xs 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 each coordinate direction
                   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      (real, 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 coordinate values to be calculated for the
                   output surface.

       mo          (integer, input) The number of Y coordinate values to be  calculated  for  the
                   output surface.

       xo          (real,  input)  An array dimensioned for no containing the X coordinate values
                   for the output grid.

       yo          (real, output) An array dimensioned for mo containing the Y coordinates of the
                   output grid.

       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_csa2xs is called to find an approximating cubic spline surface for two-dimensional input
       data.  c_csa2xs 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_csa2s.

       c_csa2xs returns a pointer to a linear array of data that is the approximated grid  stored
       in row-major order. That is, if out is declared as

         float *out;

       and we set:

       out = c_csa2xs(ni, xi, yi, zi, wts, knots, smth, nderiv,
                      no, mo, xo, yo, &ier);

       then out[i*mo+j] is the approximated function value at coordinate point (xo[i], yo[j]) for
       0 <= i < no and 0 <= j < mo. The space for out is allocated internal to c_csa2xs and is no
       * mo floats in size.

ACCESS

       To use c_csa2xs, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, c_csa2s, c_csa2ls, c_csa2lxs

       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.