CSA3S - cubic spline approximation, simple entry for three-dimensional input

       To use CSA3XS, 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                                     CSA3S(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 - 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.

       KNOTS       (integer, input) An array dimensioned for 3 containing the number of knots to be used in each
                   coordinate  direction for constructing the approximation spline.  KNOTS(I) must be at least 4
                   for I=1,3.  The larger the value 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.

       NZO         (integer, input) The number of Z 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.

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

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

       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.

       CSA3S - cubic spline approximation, simple entry for three-dimensional input

       csagrid, csa3xs, csa3ls, csa3lxs

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

       CALL CSA3S (NI, XI, UI, KNOTS, NXO, NYO, NZO, XO, YO, ZO,
                   UO, NWRK, WORK, IER)

       CSA3S is called to find an approximating cubic spline for three-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 CSA3S.