program prog2
      implicit none

      double precision xex,xe,x2rk,x4rk,t,dt,tfinish,k1,k2,k3,k4,f

      dt = 0.125
      xe = 0
      x2rk = 0
      x4rk = 0
      tfinish = 10

      open(13,file="data.d")

      do 10 t=0,tfinish,dt
         xex = 1 + (-exp(-t) - cos(t) + sin(t))/2.0
         write(13,11) t,xex,xe,x2rk,x4rk,xe-xex,x2rk-xex,x4rk-xex
         xe = xe + f(xe,t)*dt
         x2rk = x2rk + (f(x2rk,t) +
     c        f(x2rk + f(x2rk,t)*dt,t+dt))*dt/2.0
         k1 = f(x4rk,t)*dt
         k2 = f(x4rk + 0.5*k1,t+0.5*dt)*dt
         k3 = f(x4rk + 0.5*k2,t+0.5*dt)*dt
         k4 = f(x4rk + k3    ,t+dt)*dt
         x4rk = x4rk + (k1+2.0*k2+2*k3+k4)/6.0
 10   continue
 11   format(8(f12.8))
      close(13)
      stop
      end

      double precision function f(x,t)
      double precision x,t
      f = sin(t) + 1 - x
      return
      end