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.

UNIX                                              January 1999                                   CSA3LXS(3NCARG)