NAME

       CSA1XS - cubic spline approximation, expanded entry for one-dimensional input

SYNOPSIS

       CALL CSA1XS (NI, XI, YI, WTS, KNOTS, SMTH, DERIV, NO, XO, YO, NWRK, WORK, IER)

DESCRIPTION

       NI          (integer,input)  The  number of input data points. It must be that NI > 3 and,
                   depending on the size of KNOTS below, NI may have to be larger.

       XI          (real, input) An array dimensioned for NI containing the X coordinates of  the
                   input data points.

       YI          (real,  input)  An  array dimensioned for NI containing function values at the
                   input XI values, that is, YI(L) is the value of the input  function  at  XI(L)
                   for L=1,NI.

       WTS         (real, input) An array dimensioned for NI containing weights for the YI values
                   at the input XI values, that is, WTS(L) is a weight for the value of YI(L) for
                   L=1,NI.   If  you do not desire to weight the input YI 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  CSA1XS  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  must  be at least 4.  The larger the value 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)  Specifies  whether  you  want functional values (NDERIV=0),
                   first derivative values (NDERIV=1), or second derivative values (NDERIV=2).

       NO          (integer, input) The number of values to be calculated for the output curve.

       XO          (real, input) An array dimensioned for NO containing the X coordinates of  the
                   output curve.

       YO          (real,  output) An array dimensioned for NO containing the calculated function
                   values for the output curve.

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

       CSA1XS  is  called  to  find an approximating cubic spline for one-dimensional input data.
       CSA1XS 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 CSA1S.

ACCESS

       To use CSA1XS, load the NCAR Graphics library ngmath.

SEE ALSO

       csagrid, csa1s, csa1ls, csa1lxs

       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.