debugging old fortran code - debugging

Question

I have an old Fortran code for calculation of Lyapunov exponent which I tried converting to modern Fortran syntax.
PROGRAM ODE
integer, PARAMETER :: N=3
integer, PARAMETER :: NN=12
EXTERNAL FCN
DIMENSION Y(NN),ZNORM(N),GSC(N),CUM(N),C(24),W(NN,9)
Y(1) = 10.0
Y(2) = 1.0
Y(3) = 0.0
! INITIAL CONDITIONS FOR LINEAR SYSTEM (ORTHONORMAL FRAME)
DO 10 I = N+1,NN
Y(I) = 0.0
10 CONTINUE
DO 20 I = 1,N
Y((N+1)*I) = 1.0
CUM(I) = 0.0
20 CONTINUE
! INTEGRATION TOLERANCE, # OF INTEGRATION STEPS,
! TIME PER STEP, AND I/O RATE
write (*,*) "TOL, NSTEP, STPSZE, IO ?"
read (*,*) TOL, NSTEP, STPSZE, IO
! INITIALIZATION FOR INTEGRATOR
NEQ = NN
X=0.0
IND = 1
DO 100 I = 1,NSTEP
XEND = STPSZE*FLOAT(I)
! CALL ANY ODE INTEGRATOR - THIS IS AN LMSL ROUTINE
CALL DVERK (NEQ,FCN,X,Y,XEND,TOL, IND,C,NEQ,W,IER)
! CONSTRUCT A NEW ORTHONORMAL BASIS BY GRAM-SCHMIDT METHOD
! NORMALIZE FIRST VECTOR
ZNORM(1) = 0.0
DO 30 J = 1,N
ZNORM(1) = ZNORM(1)+Y(N*J+1)**2
30 CONTINUE
ZNORM(1) = SQRT(ZNORM(1))
DO 40 J = 1,N
Y(N*J+1) = Y(N*J+1)/ZNORM(1)
40 CONTINUE
! GENERATE THE NEW ORTHONORMAL SET OF VECTORS.
DO 80 J = 2,N
! GENERATE J-1 GSR COEFFICIENTS.
DO 50 K = l,(J-l)
GSC(K) = 0.0
DO 50 L = 1,N
GSC(K) = GSC(K)+Y(N*L+J)*Y(N*L+K)
50 CONTINUE
! CONSTRUCT A NEW VECTOR.
DO 60 K = 1,N
DO 60 L = l,(J-l)
Y(N*K+J) = Y(N*K+J)-GSC(L)*Y(N*K+L)
60 CONTINUE
! CALCULATE THE VECTOR'S NORM
ZNORM(J) = 0.0
DO 70 K = I,N
ZNORM(J) = ZNORM(J)+Y(N*K+J)**2
70 CONTINUE
ZNORM(J) = SQRT(ZNORM(J))
! NORMALIZE THE NEW VECTOR.
DO 80 K = 1,N
Y(N*K+J) = Y(N*K+J)/ZNORM(J)
80 CONTINUE
! UPDATE RUNNING VECTORMAGNITUDES
DO 90 K = 1,N
CUM(K) = CUM(K)+ALOG(ZNORM(K) )/ALOG(2. )
90 CONTINUE
! NORMALIZE EXPONENT AND PRINT EVERY IO ITERATIONS
IF (MOD(I,IO).EQ.0) write (*,*) X,(CUM(K)/X,K = I,N)
100 CONTINUE
CALL EXIT
END
SUBROUTINE FCN (N,X,Y,YPRIME)
! USER DEFINED ROUTINE CALLED BY IMSL INTEGRATOR.
DIMENSION Y(12),YPRIME(12)
! LORENZ EQUATIONS OF MOTION
YPRIME(1) = 16.*(Y(2)-Y(1))
YPRIME(2) = -Y(1)*Y(3)+45.92*Y(1)-Y(2)
YPRIME(3) = Y(1)*Y(2)-4.*Y(3)
! 3 COPIES OF LINEARIZED EQUATIONS OF MOTION.
DO 10 I = 0,2
YPRIME(4+I) = 16.*(Y(7+I)-Y(4+I))
YPRIME(7+I) = (45.92-Y(3))*Y(4+I)-Y(7+I)-Y(1)*Y(10+I)
YPRIME(10+I) = Y(2)*Y(4+I)+Y(1)*Y(7+I)-4.*Y(10+I)
10 CONTINUE
RETURN
END
I have debugged most of this, but I am still left with a few errors that I am unable to get around. The error log says:
main.f95:44.14:
DO 50 L = 1,N
1
Warning: Obsolescent feature: Shared DO termination label 50 at (1)
main.f95:49.18:
DO 60 L = l,(J-l)
1
Warning: Obsolescent feature: Shared DO termination label 60 at (1)
main.f95:59.14:
DO 80 K = 1,N
1
Warning: Obsolescent feature: Shared DO termination label 80 at (1)
/tmp/ccfI69Sj.o: In function `MAIN__':
main.f95:(.text+0x296): undefined reference to `dverk_'
main.f95:(.text+0x844): undefined reference to `exit_'
collect2: error: ld returned 1 exit status
Could someone please help me out in resolving the errors?
Thanks.

Answer 1

It's just what the compiler states:
Shared DO termination label
The nested loop 50 uses the same termination label:
DO 50 K = l,(J-l)
GSC(K) = 0.0
DO 50 L = 1,N
GSC(K) = GSC(K)+Y(N*L+J)*Y(N*L+K)
50 CONTINUE
In modern Fortran, you should use separate enddo statements:
DO K = l,(J-l)
GSC(K) = 0.0
DO L = 1,N
GSC(K) = GSC(K)+Y(N*L+J)*Y(N*L+K)
ENDDO
ENDDO
This omits the loop-label, but in your code you don't need it (I guess).
The same needs to be done with loops 60 and 80
The real errors are the undefined references to dverk and exit. These subroutines are missing in your code, so I assume they are contained in external objects/libraries. You need to tell the compiler where to find them, or include them in your code (after the end of the program or inside a module).