NAME

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

SYNOPSIS

       CALL CSA3S (NI, XI, UI, KNOTS, NXO, NYO, NZO, 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.

       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.

USAGE

       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.

ACCESS

       To use CSA3XS, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, csa3xs, csa3ls, csa3lxs

       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.