subroutine comp3 (fn, dfn, xstart, xend, xincr, ystart, yend,
     1  yincr, zstart, zend, zincr, fname)
c august 1979 edition. w. fullerton, c3, los alamos scientific lab.
      double precision dfn, xstart, xend, xincr, ystart, yend, yincr,
     1  zstart, zend, zincr, dx, dy, dz, df
      integer fname(1), fmt(23)
      external fn, dfn, i1mach
c
      call s9comp (48, 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, 12x, 1hy, 12x, 1hz, 69x, 4haerr, 7x, 4hrerr)
c
      aerrmx = 0.0
      rerrmx = 0.0
      do 50 i=1,11
        dx = xstart + dble(float(i-1))*xincr
        if (dx.gt.xend) go to 60
c
        do 40 j=1,11
          dy = ystart + dble(float(j-1))*yincr
          if (dy.gt.yend) go to 50
c
          write (iwunit, 20)
          do 30 k=1,11
            dz = zstart + dble(float(k-1))*zincr
            if (dz.gt.zend) go to 40
c
            x = dx
            y = dy
            z = dz
            f = fn (x, y, z)
            df = dfn (dble(x), dble(y), dble(z))
            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, dy, dz)
c
            write (iwunit, 20) x, y, z, f, df, aerr, rerr
 20         format (1x, 3e13.5, e22.14, d36.28, 2x, 2e11.3)
 30       continue
 40     continue
 50   continue
c
 60   write (iwunit, 70) aerrmx, rerrmx
 70   format (/100x, 2e11.3)
c
      return
      end