subroutine comp1 (fn, dfn, xstart, xend, xincr, fname)
c august 1979 edition. w. fullerton, c3, los alamos scientific lab.
      double precision dfn, xstart, xend, xincr, dx, df
      integer fname(1), fmt(23)
      external fn, dfn, i1mach
c
      call s9comp (26, fmt, nwd)
      iwunit = i1mach(2)
      write (iwunit, 5)
 5    format (1h1)
      write (iwunit, fmt) (fname(i), i=1,nwd), (fname(i), i=1,nwd)
      write (iwunit, 10)
 10   format (1h+, 8x, 1hx, 78x, 4haerr, 8x, 4hrerr)
c
      aerrmx = 0.0
      rerrmx = 0.0
      do 30 i=1,101
        dx = xstart + dble(float(i-1))*xincr
        if (dx.gt.xend) go to 40
c
        x = dx
        f = fn(x)
        df = dfn(dble(x))
        aerr = df - dble(f)
        rerr = 0.0
        if (df.ne.0.0d0) rerr = abs (aerr/sngl(df))
c
        aerrmx = amax1 (abs(aerr), aerrmx)
        rerrmx = amax1 (rerr, rerrmx)
        df = dfn(dx)
c
        if (mod(i,10).eq.1) write (iwunit, 20)
        write (iwunit, 20) x, f, df, aerr, rerr
 20     format (1x, e13.5, e25.15, d40.30, 3x, 2e12.3)
 30   continue
c
 40   write (iwunit, 50) aerrmx, rerrmx
 50   format (/82x, 2e12.3)
c
      return
      end