program rquadt
      integer k
      double precision dr,r,ra,t,sl,eps,pi
      open(12,file='rexp')
      pi = 4.D0*datan(1.D0)
      dr = 2.D-5
      sl = 1.D-2
      r = 5.D-2
      eps = 5.D-3
      t = 0.D0
      do 10 k=1,3000
         write(12,101) t,pi*r*r
         ra = r + 0.5D0*dr
         t = t + dr*dexp(eps/ra)/sl
         r = r + dr
 10   continue
 101  format(2(f14.10,2x))
      end