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.