我编了一个子例行程序，当主程序段调用的时候显示数组越界。

主程序段部分
ISTEP是时间步循环，MTF是我编写的子例行程序

调试的时候发现在运行的过程中ISTEP=1120403456

但是在时间步是由外界输入的，最多NSTEP=20000

不知道为什么会变成这样 求解答！！！



DO 500 ISTEP=1,NSTEP

      CALL EXPLIT (ACCEH,ACCEV,AFACT,AZERO,AALFA,BZERO,DTIME,
     &            DTEND,FORCE,IFIXD,IFPRE,IFUNC,ISTEP,NDOFN,NPOIN,OMEGA,
     &             RESID,TDISP,VELOC,YMASS,SDISP)
    
    CALL MTF(SDISP,TDISP,ISTEP,DTIME,BOUND)    
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SUBROUTINE MTF(SDISP,TDISP,ISTEP,DTIME,BOUND)
    REAL S,CA,U(400,20000,2),DX,T11,T12,T13,TDISP(400)
    REAL T21,T22,T23,T24,T25,BOUND(33,5),SDISP(400,2)
    INTEGER IBOUN,J,IDOFN,NBOUN,I,BNODE

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CC                                                                      cc
CC  THIS SUBROUTINE IS ARTIFICIAL BOUNDRY CONDITIONS                    cc
CC                                                                      cc
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC


    IF (ISTEP.LE.2) GO TO 60    


    NBOUN=33

    DX=10.0
    CA=0.001
    S=(CA*DTIME)/DX
    
    T11=(2-S)*(1-S)/2
    T12=S*(2-S)
    T13=S*(S-1)/2
    
    T21=T11*T11
    T22=2*T11*T12
    T23=2*T11*T13+T12*T12
    T24=2*T12*T13
    T25=T13*T13
    
    DO 10 IBOUN=1,NBOUN
    
    READ(10,*) (BOUND(IBOUN,J),J=1,5)

10    CONTINUE
    

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CC    提取边界点P时刻与P-1时刻的位移值      CC
CC     从第三时步开始                       CC  
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
    DO 30 IBOUN=1,NBOUN
      DO 30 J=1,5

    BNODE=(BOUND(IBOUN,J)-1)*2+1

         U(BOUND(IBOUN,J),ISTEP-2,1)=SDISP(BNODE,1)
         U(BOUND(IBOUN,J),ISTEP-1,1)=SDISP(BNODE,2)

    BNODE=BNODE+1

       U(BOUND(IBOUN,J),ISTEP-2,2)=SDISP(BNODE,1)
         U(BOUND(IBOUN,J),ISTEP-1,2)=SDISP(BNODE,2)

30    CONTINUE

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CC   从第三时步起计算边界位移值   CC 
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC    
    DO 40 IBOUN=1,NBOUN
        DO 40 I=1,2

            U(BOUND(IBOUN,1),ISTEP,I)=T11*U(BOUND(IBOUN,1),ISTEP-1,I)+
     &T12*U(BOUND(IBOUN,2),ISTEP-1,I)+T13*U(BOUND(IBOUN,3),ISTEP-1,I)+
     &T21*U(BOUND(IBOUN,1),ISTEP-2,I)+T22*U(BOUND(IBOUN,2),ISTEP-2,I)+
     &T23*U(BOUND(IBOUN,3),ISTEP-2,I)+T24*U(BOUND(IBOUN,4),ISTEP-2,I)+
     &T25*U(BOUND(IBOUN,5),ISTEP-2,I)

40    CONTINUE

CCCCCCCCCCCCCCCCCCCCCCCCCC
CC   导出边界点位移值   CC
CCCCCCCCCCCCCCCCCCCCCCCCCC
    DO 50 IBOUN=1,NBOUN

          BNODE=(BOUND(IBOUN,1)-1)*2+1
            TDISP(BNODE)= U(BOUND(IBOUN,1),ISTEP,1)
    

            BNODE=BNODE+1
            TDISP(BNODE)= U(BOUND(IBOUN,1),ISTEP,2)

    
50    CONTINUE
    
    
60    CONTINUE
      END
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