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