NAME

       CSA2LXS - cubic spline approximation, expanded entry for two-dimensional input, list output

SYNOPSIS

       CALL CSA2LXS (NI, XI, UI, WTS, KNOTS, SMTH, NDERIV,
                     NO, XO, YO, 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 coordinates of  the  input  data  points.  XI  is
                   dimensioned  for 2 x NI.  XI(1,L) is the X coordinate and XI(2,L) is the Y 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 the coordinate (XI(1,L),XI(2,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 CSA2LXS 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  2 and provides the number of knots to be used in the X and the Y
                   directions.  Both KNOTS(1) and KNOTS(2) must be at least 4.  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 2 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.

       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)) for I=1,NO.

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

       CSA2LXS 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 CSA2LS.

ACCESS

       To use CSA2LXS, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, csa2s, csa2xs, csa2ls,

       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.