[其他行业算法] 简单力场下粒子边界条件设置

        program main
        INTEGER*4 MTIME, MXPARM,NP, IDO, MC, istep
        PARAMETER (MXPARM=50,MTIME=5000000000, NP=50)
        REAL*8 Y(NP),YPRIME(NP)
        REAL*8 PARAM(MXPARM)
        real*8 t_stop, t_start,del_t
        REAL*8 TOL,T1,T2
        COMMON /blk/a
        external DIVPRK,DSET,FCN
        t_start=0d0
        t_stop=7d0
        del_t=0.1d0
        TOL=1.0D-3
ccccc初值:y(1)=x0=-12,y(2)=v0=3
        y(1)=-12
        y(2)=3
      CALL DSET(MXPARM, 0.0D0, PARAM, 1)
        PARAM(10)=1.0D0
        PARAM(4)=MTIME+1
        istep=0
        IDO=1
        T1=T_START
        mt=0
110        CONTINUE
c
        istep=istep+1
        T2=T1+DEL_T
        CALL DIVPRK(IDO,NP,FCN,T1,T2,TOL,PARAM,Y)
        write(*,*)t2,y(2),y(1)
              IF(T2<=T_STOP) GOTO 110
        print *,'end'
        stop
        end
      subroutine FCN (NP, T2, Y, YPRIME)
      INTEGER*4 NP
        REAL*8 Y(NP),YPRIME(NP)
      COMMON /blk/a
        a=2
      YPRIME(1) = Y(2)
      YPRIME(2) = a
      return
      end subroutine