program numerical2

      real x(2),t,dt
      open(unit=13,file="data.d")
      dt  = 0.25

      x(1) = 1
      x(2) = 0

      do 10 t=0,25,dt
         write(13,*) t,x(1),x(2),exp(-t)
         x(1) = x(1) + x(2)*dt
         x(2) = x(2) - t*x(1)*dt
 10   continue

      end