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.