Question

我是Fortran的完整入门者，并且正在研究通过使用微分方程求解器在不同时间步求解微分方程来求解动力学机制的代码。这是下载整个项目的zip文件的链接：

http://www.filedropper.com/fortranmicropyrolyzersetup

微分求解器的输入变量在代码中定义如下：

     ! Declaration of variables
     implicit none
     EXTERNAL                   ::  FEXSB_AUTO, JEX_SB
     integer                    ::  neq,Mf,lrw,liw,iwork,itol,itask,istate,iopt     !solver parameters                
     integer                    ::  j,jjk,m                                         !Counters
     double precision           ::  ATOL,RTOL, RWORK                                !solver parameters
     double precision           ::  T, TOUT                                         !starting time (s), timestep time (s)
     double precision           ::  Y, w                                            !molar fraction of biomass (-), mass fraction of biomass (-)
     double precision           ::  y_gas, w_gas, Conc                              !molar fraction in gas phase (-), concentration in gas phase (mol/m³), mass fraction in gas phase (-)
     double precision           ::  n(speciescount)                                 !number of moles (used temporarily to calculate initial molar fracions)  
     character*5                ::  simulationNumber


  !Setting the solver parameters
     neq = SpeciesCount         !number of equations
     ITOL = 1                   !RTOL and ATOL are integers
     RTOL = 1.0D-8               !Relative tolerance
     ATOL = 1.0D-15              !Absolute tolerance
     ITASK = 1                  
     ISTATE = 1
     LRW = 22 +  9*SpeciesCount + 2*SpeciesCount**2                  !Array sizing (see VODE)
     LIW = 30+SpeciesCount                                         !Array sizint (see VODE)
     MF = 22                    !Use BDF with finite difference Jacobian
     IOPT = 1                   !Optional input specified
     Iwork(6) = 7000            !Increase maximum iteration steps from 500 to 2000 otherwise the solver does not converge

然后在每个时间步的do循环中调用微分求解器，如下所示：

  ! Solve reactor equations (see FEXSB) and advance time, until stop criterium is met
     TimeStep = 0   ! dimensionless time step
     !DO while(wm(1).lt.0.9999) -> previously used stop criterium
     DO while((y_gas(1).lt.0.99999).OR.(TimeStep.lt.10))        !stop criterium: molar fraction Helium = 0.9999 AND do at least 100 timesteps
         TimeStep = TimeStep + 1
         write(*,*)"Doing iteration for time step",TimeStep
         call DVODE(FEXSB_AUTO,NEQ,Y,T,TOUT,ITOL,RTOL,ATOL,ITASK,ISTATE,IOPT,RWORK,LRW,IWORK,LIW,JEX_SB,MF)     !solve reactor equations to Y
        !CALL DVODE(FEXSB_AUTO,NEQ,Y,T,TOUT,ITOL,RTOL,ATOL,ITASK,ISTATE,IOPT,RWORK,LRW,IWORK,LIW,JEX_SB,MF,RPAR,IPAR)

        ! calculate w, y_gas, w_gas and Conc from Y
        do j = 1, SpeciesCount

            if (Y(j) .lt. 1.0D-10) then      ! round to zero below 10e-10 to avoid negative numbers and numerical problems with small numbers
                Y(j) = 0.0D0
            endif
            if (MolarFlowRate(j) .lt. 1.0D-10) then
                MolarFlowRate(j) = 0.0D0
            endif
            w(j) = Y(j)*n0_tot*amms(j) / (mass_sample)
            y_gas(j) = MolarFlowRate(j) / TotalMolarFlowRate
            w_gas(j) = MolarFlowRate(j)*amms(j) / (1000*MassFlowRate) ! factor 1000 to put molar mass in kg/mol instead of g/mol
            Conc(j) = MolarFlowRate(j) / VolumetricFlowRate

        end do

微分方程求解器无法成功完成行的do循环：

DO while((y_gas(1).lt.0.99999).OR.(TimeStep.lt.10))

在该行中调用ODE Solver时，似乎是第一次识别变量：

call DVODE(FEXSB_AUTO,NEQ,Y,T,TOUT,ITOL,RTOL,ATOL,ITASK,ISTATE,IOPT,RWORK,LRW,IWORK,LIW,JEX_SB,MF)

求解器成功完成了第一次迭代。时间步长再增加一次之后，调用函数将再次运行，但是这次无法以某种方式识别变量。当我在第一步之后停止调试错误代码的过程时，我意识到DVODE所需的变量不再具有设置值，而是在第一次成功迭代后就被删除了。

什么可能导致此问题？

*DECK DVODE
      SUBROUTINE DVODE (F, NEQ, Y, T, TOUT, ITOL, RTOL, ATOL, ITASK,
     1            ISTATE, IOPT, RWORK, LRW, IWORK, LIW, JAC, MF,
     2            RPAR, IPAR)
      EXTERNAL F, JAC
      DOUBLE PRECISION Y, T, TOUT, RTOL, ATOL, RWORK, RPAR
      INTEGER NEQ, ITOL, ITASK, ISTATE, IOPT, LRW, IWORK, LIW,
     1        MF, IPAR
      DIMENSION Y(*), RTOL(*), ATOL(*), RWORK(LRW), IWORK(LIW),
     1          RPAR(*), IPAR(*)
!-----------------------------------------------------------------------
c dvode: Variable-coefficient Ordinary Differential Equation solver,
! with fixed-leading-coefficient implementation.
! This version is in double precision.
!
! DVODE solves the initial value problem for stiff or nonstiff
! systems of first order ODEs,
!     dy/dt = f(t,y) ,  or, in component form,
!     dy(i)/dt = f(i) = f(i,t,y(1),y(2),...,y(NEQ)) (i = 1,...,NEQ).
! DVODE is a package based on the EPISODE and EPISODEB packages, and
! on the ODEPACK user interface standard, with minor modifications.
!-----------------------------------------------------------------------
! Authors:
!               Peter N. Brown and Alan !. Hindmarsh
!               Center for Applied Scientific Computing, L-561
!               Lawrence Livermore National Laboratory
!               Livermore, CA 94551
! and
!               George D. Byrne
!               Illinois Institute of Technology
!               Chicago, IL 60616
!-----------------------------------------------------------------------

任何帮助将不胜感激。请注意，我是Fortran的新手。如果我想提供任何其他信息来帮助您回答我的问题，请随时与我们联系。预先感谢！

Answer 1

在第一次迭代后应该不修改参数的假设是错误的。

在fortran函数中，参数始终通过引用传递。因此，fortran函数从不保证调用后原始参数集相同。 DO更改参数可能是功能的预期（或较差）设计。仅文档可以为您提供帮助，而您在问题中提供的信息还不够，这很可能也意味着：可能没有足够的文档来说明这种情况/功能。

与fortran中的C / C ++相比，没有用于变量的“ const”修饰符，这些修饰符可以保证您现在必须假设的内容。

在我看来，唯一的解决方案是在每次调用DVODE之前重新初始化所有参数。

Fortran

1 个答案: