implicit none

      real x1,x2,t,dt,w,tfinish

      open(unit=13,file="data.d")
      
      x1 = 0
      x2 = 0

      tfinish = 30
      dt = 0.01
      w = 1

      write(13,*) t,x1,x2
      do 10 t=0,tfinish,dt
         x1 = x1 + (x2)*dt
         x2 = x2 + (-x1+sin(w*t))*dt
         write(13,*) t,x1,x2
 10   continue

      end