NAME

       CSA3LXS  -  cubic  spline  approximation, expanded entry for three-dimensional input, list
       output

SYNOPSIS

       CALL CSA3LXS (NI, XI, UI, WTS, KNOTS, SMTH, NDERIV,
                     NO, XO, YO, ZO, UO, NWRK, WORK, IER)

DESCRIPTION

       NI          (integer,input) The number of input data points. It must be  that  NI  .gt.  3
                   and, depending on the size of KNOTS below, NI may have to be larger.

       XI          (real,  input) An array containing the X - Y - Z coordinates of the input data
                   points.  XI is dimensioned for 3 x NI.  XI(1,L) is the X  coordinate,  XI(2,L)
                   is  the Y coordinate, and XI(2,L) is the Z coordinate for the input domain for
                   L=1,NI.

       UI          (real, input) An array dimensioned for NI containing function  values  at  the
                   input  XI  values,  that is, UI(L) is the value of the input function at XI(L)
                   for L=1,NI.

       WTS         (real, input) An array dimensioned for NI containing weights for the UI values
                   at the input XI values, that is, WTS(L) is a weight for the value of UI(L) for
                   L=1,NI.  If you do not desire to weight the input UI values, then  set  WTS(1)
                   to  -1.   The weights in the WTS array are relative and may be set to any non-
                   negative value.  When 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 is dimensioned for 3 and provides the  number  of
                   knots  to be used in the X, Y, and  Z directions.  KNOTS(I) must be at least 4
                   for I=1,3.  The larger the values 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      (integer,  input)  An  array  dimensioned  for  3  that  specifies,  for  each
                   coordinate,  whether you want functional values (=0), first derivative  values
                   (=1), or second derivative values (=2).

       NO          (integer,  input)  The number of coordinate values in the output list.  NO can
                   be any positive number.

       XO          (real, input) An array dimensioned for NO containing the X coordinates of  the
                   output list.

       YO          (real,  input) An array dimensioned for NO containing the Y coordinates of the
                   output list.

       ZO          (real, input) An array dimensioned for NO containing the Z coordinates of  the
                   output list.

       UO          (real,  output) An array dimensioned for NO containing the calculated function
                   values for the output spline.  UO(I) is the  calculated  functional  value  at
                   (XO(I),YO(I),ZO(I)) for I=1,NO.

       NWRK        (integer,  input)  The  size  of  the  WORK array.  NWRK must be at least NK *
                   (NK+3) where NK = KNOTS(1) * KNOTS(2) * KNOTS(3).

       WORK        (real, input) A work array dimensioned for NWRK.

       IER         (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 man page for
                   csagrid_errors for details.

USAGE

       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 CSA3LS.

ACCESS

       To use CSA3LXS, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, csa3s, csa3xs, csa3ls

       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.