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.

UNIX                                              January 1999                                 c_csa3lxs(3NCARG)