CSA2S - cubic spline approximation, simple entry for two-dimensional input, gridded output

       To use CSA2S, load the NCAR Graphics library ngmath.

       Copyright (C) 2000
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.

UNIX                                              January 1999                                     CSA2S(3NCARG)

       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.

       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.

       NXO         (integer, input) The number of X coordinate values in the output grid.

       NYO         (integer, input) The number of Y coordinate values in the output grid.

       XO          (real, input) An array dimensioned for  NXO  containing  the  X  coordinates  of  the  output
                   surface.

       YO          (real,  input)  An  array  dimensioned  for  NYO  containing  the Y coordinates of the output
                   surface.

       UO          (real, output) An array dimensioned for NXO x NYO containing the calculated  function  values
                   for  the  output  surface.   UO(I,J)  is the calculated functional value at (XO(I),YO(J)) for
                   I=1,NXO and J=1,NYO.

       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.

       CSA2S - cubic spline approximation, simple entry for two-dimensional input, gridded output

       csagrid, csa2xs, csa2ls, csa2lxs

       Complete documentation for Csagrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html

       CALL CSA2S (NI, XI, UI, KNOTS, NXO, ,NYO, XO, YO, UO, NWRK, WORK, IER)

       CSA2S is called to find an approximating cubic spline surface for two-dimensional  input  data.   If  you
       want  to weight the input data values, calculate derivatives, or handle data sparse areas specially, then
       you will need to use CSA2XS.