OpenMP parameter sweep parallel

问题:

I am new to OpenMP. I want to solve a stiff ODE system for a range of parameter values using parallel do loops. I use the following code in Fortran given below. However, I do not know whether calling a stiff solver(as a subroutine) inside a parallel do loop is allowed or not? Also, I want to write the time series data into files with filenames such as "r_value_s__value.txt" in the subroutine before the return to the main program. Can anyone help. Below is the code and the error. I used gfortran with flags -fopenmp to compile.

   PROGRAM OPENMP_PARALLEL_STIFF             USE omp_lib            IMPLICIT NONE             INTEGER :: I, J            INTEGER, PARAMETER :: RTOT=10, STOT=15            INTEGER :: TID            INTEGER, PARAMETER :: NUM_THREADS=8            DOUBLE PRECISION :: T_INITIAL, T_FINAL            CALL OMP_SET_NUM_THREADS(NUM_THREADS)            CALL CPU_TIME(T_INITIAL)            PRINT*, "TIME INITIAL ",T_INITIAL !$OMP PARALLEL DO PRIVATE(I,J,TID)             DO I=1,RTOT               DO J=1,STOT                 TID=OMP_GET_THREAD_NUM()                 CALL STIFF_DRIVER(TID,I,J,RTOT,STOT)               END DO            END DO !$OMP END PARALLEL DO            CALL CPU_TIME(T_FINAL)           PRINT*, "TIME FINAL ",T_FINAL           PRINT*, "TIME ELAPSED ",(T_FINAL-T_INITIAL)/NUM_THREADS        END PROGRAM OPENMP_PARALLEL_STIFF         SUBROUTINE STIFF_DRIVER(TID,II,JJ,RTOT,STOT)            USE USEFUL_PARAMETERS_N_FUNC            USE DVODE_F90_M  !     Type declarations:            IMPLICIT NONE   !     Number of odes for the problem:            INTEGER :: SERIAL_NUMBER, TID           INTEGER :: II, JJ, RTOT, STOT, IND           INTEGER :: J, NTOUT           INTEGER :: ITASK, ISTATE, ISTATS, I  !     parameters : declaration            DOUBLE PRECISION, PARAMETER :: s0=0.450D0, dr=1.0D-4, ds=1.0D-2            DOUBLE PRECISION, DIMENSION(NEQ) :: Y, YOUT           DOUBLE PRECISION :: ATOL, RTOL, RSTATS, T, TOUT, EPS, TFINAL, DELTAT           DIMENSION :: RSTATS(22), ISTATS(31)           DOUBLE PRECISION :: bb, cc, ba, ba1, eta           CHARACTER(len=45) :: filename            TYPE (VODE_OPTS) :: OPTIONS            SERIAL_NUMBER=3011+II+(JJ-1)*RTOT           IND=TID+3011+II+(JJ-1)*RTOT           WRITE (*,12)SERIAL_NUMBER,TID     12    FORMAT ("SL. NO. ",I5," THREAD NO.",I3)            r=(II-1)*dr           s=s0+JJ*ds            EPS = 1.0D-9  !         Open the output file:            WRITE (filename,93)r,s     93    FORMAT ("r_",f6.4,"_s_",f4.2,".txt")           OPEN (UNIT=IND,FILE=filename,STATUS='UNKNOWN',ACTION='WRITE')  !     Parameters for the stiff ODE system             q0 = 0.60D0;    v = 3.0D0            Va = 20.0D-4;  Vs = 1.0D-1            e1 = 1.0D-1;   e2 = 1.10D-5; e3 = 2.3D-3; e4=3.0D-4           del = 1.7D-4;   mu = 5.9D-4            al = 1.70D-4;  be = 8.9D-4;  ga = 2.5D-1  !         S and r dependent parameters             e1s = e1/s;    e2s = e2/(s**2);   e3s = e3/s;    e4s = e4/s           dels = del*s;    rs = r*s            e1v = e1/v;     e2v = e2/(v**2);   e3v = e3/v;    e4v = e4/v           delv = del*v;     rv = r*v  !         SET INITIAL PARAMETERS for INTEGRATION ROUTINES              T = 0.0D0           TFINAL = 200.0D0           DELTAT = 0.10D0           NTOUT = INT(TFINAL/DELTAT)           RTOL = EPS           ATOL = EPS           ITASK = 1           ISTATE = 1  !         Set the initial conditions: USING MODULE USEFUL_PARAMETERS_N_FUNC            CALL Y_INITIAL(NEQ,Y)  !        Set the VODE_F90 options:            OPTIONS = SET_OPTS(DENSE_J=.TRUE.,USER_SUPPLIED_JACOBIAN=.FALSE., &           RELERR=RTOL,ABSERR=ATOL,MXSTEP=100000)  !         Integration:            DO I=1,NTOUT            TOUT = (I-1)*DELTAT            CALL DVODE_F90(F_FUNC,NEQ,Y,T,TOUT,ITASK,ISTATE,OPTIONS)  !         Stop the integration in case of an error            IF (ISTATE<0) THEN             WRITE (*,*)"ISTATE ", ISTATE             STOP           END IF  !         WRITE DATA TO FILE            WRITE (IND,*) TOUT,T, Y(NEQ-2)           END DO            CLOSE(UNIT=IND)           RETURN     END SUBROUTINE STIFF_DRIVER 

At line ** of file openmp_parallel_stiff.f90 (unit = 3013) Fortran runtime error: File already opened in another unit

回答1:

The issue is the format that you chose: f6.4 for r will overflow for r>=10. Then, the output will be six asterisks ****** (depending on the compiler) for all values of r>=10 on all threads. The same holds true for s.

I would suggest to either limit/check the range of these values or extend the format to honor more digits.

---

As @francescalus mentioned, another possibility is hit a combination of II and JJ where r and s are identical.

Just for the fun of it - let's do the math:

r=(II-1)*dr s=s0+JJ*ds 

From r=s follows

(II-1)*dr = s0+JJ*ds 

or

II = 1 + s0/dr + JJ*ds/dr 

Using the constants s0=0.450D0, dr=1.0D-4, ds=1.0D-2 yields

II = 4501 + JJ*10 

So, whenever this combination is true for two (or more) threads at a time, you run into the observed issue.

Simple solution for this case: add the thread number to the file name.

文章来源: OpenMP parameter sweep parallel