NAME

       c_csa3s  -  cubic  spline approximation, simple entry for three-dimensional input, gridded
       output

FUNCTION PROTOTYPE

       float *c_csa3s(int, float [], float [], float [], float [], int [], int, int,
                      int, float [], float [], float [], int *);

SYNOPSIS

       float *c_csa3s (int n, float xi[], float yi[], float zi[],
                       float ui[], int knots[3], int nxo, int nyo,
                       int nzo, float xo[], float yo[], float zo[],
                       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 dimensioned for n containing the Z coordinate values
                   for the input function.

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

       knots       (integer,  input)  The  number  of  knots  to  be  used  in  constructing  the
                   approximation spline. knots[0], knots[1] and knots[2] must each be at least 4.
                   The larger the value for knots, the closer the approximated curve will come to
                   passing through the input function values.

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

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

       nzo         The number of Z coordinate values to be calculated for the output grid.

       xo          (real, input) An array dimensioned for nxo containing the X coordinates of the
                   output grid.

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

       zo          (real, output) An array dimensioned for nzo containing the  Z  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_csa3s  is called to find an approximating cubic spline for three-dimensional input data.
       If you want to weight the input data values, calculate derivatives, or handle data  sparse
       areas specially, then you will need to use c_csa3xs.

       c_csa3s  returns  a  pointer  to  a  linear array of data that is the approximation spline
       stored in row-major order. That is, if out is declared as

         float *out;

       and we set:

         out = c_csa3s(n, x, y, z, u, nx, ny, nz, xo, yo, zo, &ier);

       then out[nz*ny*i + nz*j + k] is the  approximation  function  value  at  coordinate  point
       (xo[i],  yo[j], zo[k]) for 0 <= i < nx, 0 <= j < ny, and 0 <= k < nz. The space for out is
       allocated internal to c_csa3s and is nx*ny*nz floats in size.

ACCESS

       To use c_csa3s, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, c_csa3xs, c_csa3ls, c_csa3lxs

       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.