[Fortran] syntaxhighlighter_viewsource syntaxhighlighter_copycode
module m_rk4_ods
    implicit  none
    integer::M=100
 contains
 subroutine solve(func,t0,tt,y0,N)
     implicit none
     external func
     integer::N
     real*8::y0(N),y(N)
     real*8::k1(N),k2(N),k3(N),k4(N)
     real*8::h,tt,t0,t
     integer::i
     h=(tt-t0)/M
t=t0
     y=y0
     do i=1,M
         call func(k1,t,y,N)
         call func(k2,t+h/2,y+h/2*k1,N)
         call func(k3,t+h/2,y+h/2*k2,N)
         call func(k4,t+h,y+h*k3,N)
         y=y+(k1+2*k2+2*k3+k4)*h/6
         t=t0+i*h
         write(11,*)t,y(1),y(2),y(3),y(4),y(5),y(6)
        100 FORMAT(1X,T3,F10.5,F12.8)
     end do
     end subroutine solve
 subroutine fun1(f,t,y,N)
     implicit none
     integer::N
     real*8::f(N),y(N)
     real*8::t,t0,tt
     f(1)=cos(t-y(6))-y(3)**2/sqrt(1+y(3)**2)*cos(t-y(6))/(3*10**8)
     f(2)=0
     f(3)=y(1)/sqrt(1+y(1)**2)*cos(t-y(6))
     f(4)=y(1)/sqrt(1+y(1)**2)
     f(5)=y(2)/sqrt(1+y(2)**2)
     f(6)=y(3)/sqrt(1+y(3)**2)
 end subroutine fun1
     end module m_rk4_ods
 program main  
     use m_rk4_ods
 implicit none
     integer::N
     real*8::y(6),y0(6)
     real*8::t0,tt
     open(unit=11,file='result10.txt')
     N=6
     t0=0.0
     tt=12.0
     y0=(/0,0,0,0,0,0/)
     call solve(fun1,t0,tt,y0,N)
     end program main