NAME

       c_csa3lxs  -  cubic spline approximation, expanded entry for three-dimensional input, list
       output

FUNCTION PROTOTYPE

       float *c_csa3lxs(int, float [], float [], float [], float [],
                        float [], int [], float, int [],
                        int, float [], float [], float [], int *);

SYNOPSIS

       float *c_csa3lxs(int n, float xi[], float yi[], float zi[], float ui[],
                        float wts[], int knots[3], float smth, int nderiv[3],
                        int no, 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.

       wts         (real,  input)  An  array  containing  weights  for the ui values at the input
                   values, that is, wts[l] is a weight for the value of ui[l] for l=0,n-1. If you
                   do  not  desire  to  weight  the  input  ui 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_csa3lxs  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],  knots[1], and knots[2] 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, nderiv[1]=1
                   and nderiv[2]=0, then the second order mixed partial with respect to X  and  Y
                   would be computed.

       no          (integer,  input)  The  number of X - Y - Z 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.

       zo          (real, output) An array dimensioned for no containing the Z 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_csa3lxs  is  called  to find values of an approximating cubic spline at specified three-
       dimensional coordinates.  c_csa3lxs 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_csa3ls.

       c_csa3lxs 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_csa3lxs(n, x, y, z, u, wts, knots, smth, nderiv,
                         no, xo, yo, zo, &ier);

       then  out[i]  is the approximated function value at coordinate point (xo[i], yo[i], zo[i])
       for 0 <= i < no. The space for out is allocated internal to c_csa3lxs and is no floats  in
       size.

ACCESS

       To use c_csa3lxs, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, c_csa3s, c_csa3xs, 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.