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DEM39

       SUBROUTINE  DEM39 (NIN,NOUT)
 C$    (DEM39 - Tensioned Splines)
 C$    This program illustrates the use of routines FITC1,  FITC2,
 C$    and FITD2 from ACM Algorithm 476 for interpolating a  curve
 C$    by a  spline  under  tension.   Three  examples  showing  a
 C$    decaying  sine  wave   and  its   interpolated  and   exact
 C$    derivative are  produced.   For  each,  the  original  data
 C$    points are  drawn, connected  by straight  lines, with  the
 C$    interpolated curves  for  three different  tension  factors
 C$    appearing in quadrants 2-4.  The plots produced are for
 C$
 C$    1....The function and its interpolant.
 C$    2....The derivative of the  function and the derivative  of
 C$         its interpolant.
 C$    3....The derivative of the  function and the interpolant of
 C$         its splined interpolated derivative.
 C$
 C$    The error in the interpolated function is multiplied by 100
 C$    and superimposed on each plot.
 C$    (10-APR-82)