driver3.f

This time-controlled driver shows that it is possible to terminate a run by elapsed CPU time, and yet be able to print all desired information. This driver also illustrates the use of two stopping criteria that may be used in conjunction with a limit on execution time. The sample problem used here is the same as in driver1 and driver2 (the extended Rosenbrock function with bounds on the variables). (Fortran-77 version)

c> \file driver3.f
 
c                                                                                      
c  L-BFGS-B is released under the "New BSD License" (aka "Modified BSD License"        
c  or "3-clause license")                                                              
c  Please read attached file License.txt                                               
c                                        
c                             DRIVER 3 in Fortran 77
c     --------------------------------------------------------------
c            TIME-CONTROLLED DRIVER FOR L-BFGS-B (version 3.0)
c     --------------------------------------------------------------
c
c        L-BFGS-B is a code for solving large nonlinear optimization
c             problems with simple bounds on the variables.
c
c        The code can also be used for unconstrained problems and is
c        as efficient for these problems as the earlier limited memory
c                          code L-BFGS.
c
c        This driver shows how to terminate a run after some prescribed
c        CPU time has elapsed, and how to print the desired information 
c        before exiting.
c
c     References:
c
c        [1] R. H. Byrd, P. Lu, J. Nocedal and C. Zhu, ``A limited
c        memory algorithm for bound constrained optimization'',
c        SIAM J. Scientific Computing 16 (1995), no. 5, pp. 1190--1208.
c
c        [2] C. Zhu, R.H. Byrd, P. Lu, J. Nocedal, ``L-BFGS-B: FORTRAN
c        Subroutines for Large Scale Bound Constrained Optimization''
c        Tech. Report, NAM-11, EECS Department, Northwestern University,
c        1994.
c
c
c          (Postscript files of these papers are available via anonymous
c           ftp to eecs.nwu.edu in the directory pub/lbfgs/lbfgs_bcm.)
c
c                              *  *  *
c
c         February 2011   (latest revision)
c         Optimization Center at Northwestern University
c         Instituto Tecnologico Autonomo de Mexico
c
c         Jorge Nocedal and Jose Luis Morales, Remark on "Algorithm 778: 
c         L-BFGS-B: Fortran Subroutines for Large-Scale Bound Constrained 
c         Optimization"  (2011). To appear in  ACM Transactions on 
c         Mathematical Software,
c
c
c     **************
 
      program driver
      use json_writer, only: json_write_aggregate
 
c     This time-controlled driver shows that it is possible to terminate
c     a run by elapsed CPU time, and yet be able to print all desired
c     information. This driver also illustrates the use of two
c     stopping criteria that may be used in conjunction with a limit
c     on execution time. The sample problem used here is the same as in
c     driver1 and driver2 (the extended Rosenbrock function with bounds
c     on the variables).
 
      integer          nmax, mmax
      parameter(nmax=1024,mmax=17)
c        nmax is the dimension of the largest problem to be solved.
c        mmax is the maximum number of limited memory corrections.
 
c     Declare the variables needed by the code.
c       A description of all these variables is given at the end of 
c       driver1.
 
      character*60     task, csave
      logical          lsave(4)
      integer          n, m, iprint,
     +                 nbd(nmax), iwa(3*nmax), isave(44)
      double precision f, factr, pgtol,
     +                 x(nmax), l(nmax), u(nmax), g(nmax), dsave(29),
     +                 wa(2*mmax*nmax+5*nmax+11*mmax*mmax+8*mmax)
 
c     Declare a few additional variables for the sample problem
c       and for keeping track of time.
 
      double precision t1, t2, time1, time2, tlimit
      integer          i, j
 
c     Test instrumentation: dump per-iteration state to JSON when the
c     environment variable LBFGSB_JSON_OUTPUT is set. No-op otherwise.
c     LBFGSB_TLIMIT optionally overrides tlimit for reproducibility.
      character*512    lbfgsb_json
      character*64     env_tlimit
      logical          json_active
 
c     We specify a limite on the CPU time (in seconds).
 
      tlimit = 0.2
      call get_environment_variable('LBFGSB_TLIMIT', env_tlimit)
      if (len_trim(env_tlimit) .gt. 0) read(env_tlimit, *) tlimit
 
c     We suppress the default output.  (The user could also elect to 
c       use the default output by choosing iprint >= 0.)
 
      iprint = -1
 
c     We suppress the code-supplied stopping tests because we will
c       provide our own termination conditions
 
      factr=0.0d0
      pgtol=0.0d0
 
c     We specify the dimension n of the sample problem and the number
c        m of limited memory corrections stored.  (n and m should not
c        exceed the limits nmax and mmax respectively.)
 
      n=1000
      m=10
 
c     We now specify nbd which defines the bounds on the variables:
c                    l   specifies the lower bounds,
c                    u   specifies the upper bounds. 
 
c     First set bounds on the odd-numbered variables.
 
      do 10 i=1,n,2
         nbd(i)=2
         l(i)=1.0d0
         u(i)=1.0d2
  10  continue
 
c     Next set bounds on the even-numbered variables.
 
      do 12 i=2,n,2
         nbd(i)=2
         l(i)=-1.0d2
         u(i)=1.0d2
  12   continue
 
c     We now define the starting point.
 
      do 14 i=1,n
         x(i)=3.0d0
  14  continue
 
c     We now write the heading of the output.
 
      write (6,16)
  16  format(/,5x, 'Solving sample problem.',
     +       /,5x, ' (f = 0.0 at the optimal solution.)',/) 
 
c     We start the iteration by initializing task.
c
      task = 'START'
 
c     Test instrumentation: enabled when LBFGSB_JSON_OUTPUT is set.
      call get_environment_variable('LBFGSB_JSON_OUTPUT', lbfgsb_json)
      json_active = (len_trim(lbfgsb_json) .gt. 0)
 
c        ------- the beginning of the loop ----------
 
c     We begin counting the CPU time.
 
      call timer(time1)
 
 111  continue
 
c     This is the call to the L-BFGS-B code.
 
      call setulb(n,m,x,l,u,nbd,f,g,factr,pgtol,wa,iwa,task,iprint,
     +            csave,lsave,isave,dsave)
 
      if (task(1:2) .eq. 'FG') then
c        the minimization routine has returned to request the
c        function f and gradient g values at the current x.
c        Before evaluating f and g we check the CPU time spent.
 
         call timer(time2)
         if (time2-time1 .gt. tlimit) then
            task='STOP: CPU EXCEEDING THE TIME LIMIT.'
 
c          Note: Assigning task(1:4)='STOP' will terminate the run;
c          setting task(7:9)='CPU' will restore the information at
c          the latest iterate generated by the code so that it can
c          be correctly printed by the driver.
 
c          In this driver we have chosen to disable the
c          printing options of the code (we set iprint=-1);
c          instead we are using customized output: we print the
c          latest value of x, the corresponding function value f and
c          the norm of the projected gradient |proj g|.
 
c          We print out the information contained in task.
 
            write (6,*) task
 
c          We print the latest iterate contained in wa(j+1:j+n), where
c 
            j = 3*n+2*m*n+11*m**2
            write (6,*) 'Latest iterate X ='
            write (6,'((1x,1p, 6(1x,d11.4)))') (wa(i),i = j+1,j+n) 
 
c          We print the function value f and the norm of the projected
c          gradient |proj g| at the last iterate; they are stored in
c          dsave(2) and dsave(13) respectively.
 
            write (6,'(a,1p,d12.5,4x,a,1p,d12.5)')
     +         'At latest iterate   f =',dsave(2),'|proj g| =',dsave(13)
 
         else
 
c          The time limit has not been reached and we compute
c          the function value f for the sample problem.
 
            f=.25d0*(x(1)-1.d0)**2
            do 20 i=2,n
               f=f+(x(i)-x(i-1)**2)**2
  20        continue
            f=4.d0*f
 
c          Compute gradient g for the sample problem.
 
            t1=x(2)-x(1)**2
            g(1)=2.d0*(x(1)-1.d0)-1.6d1*x(1)*t1
            do 22 i=2,n-1
               t2=t1
               t1=x(i+1)-x(i)**2
               g(i)=8.d0*t2-1.6d1*x(i)*t1
  22        continue
            g(n)=8.d0*t1
 
         endif
 
c          go back to the minimization routine.
         goto 111
      endif
c
      if (task(1:5) .eq. 'NEW_X') then        
c        the minimization routine has returned with a new iterate.
c        The time limit has not been reached, and we test whether
c        the following two stopping tests are satisfied:
 
c        1) Terminate if the total number of f and g evaluations
c             exceeds 900.
 
         if (isave(34) .ge. 900)
     +      task='STOP: TOTAL NO. of f AND g EVALUATIONS EXCEEDS LIMIT'
 
c        2) Terminate if  |proj g|/(1+|f|) < 1.0d-10.
 
         if (dsave(13) .le. 1.d-10*(1.0d0 + abs(f)))
     +      task='STOP: THE PROJECTED GRADIENT IS SUFFICIENTLY SMALL'
 
c        We wish to print the following information at each iteration:
c          1) the current iteration number, isave(30),
c          2) the total number of f and g evaluations, isave(34),
c          3) the value of the objective function f,
c          4) the norm of the projected gradient,  dsve(13)
c
c        See the comments at the end of driver1 for a description
c        of the variables isave and dsave.
 
         
         write (6,'(2(a,i5,4x),a,1p,d12.5,4x,a,1p,d12.5)') 'Iterate'
     +      ,isave(30),'nfg =',isave(34),'f =',f,'|proj g| =',dsave(13)
 
c        If the run is to be terminated, we print also the information
c        contained in task as well as the final value of x.
 
 
         if (task(1:4) .eq. 'STOP') then
            write (6,*) task  
            write (6,*) 'Final X='
            write (6,'((1x,1p, 6(1x,d11.4)))') (x(i),i = 1,n)
         endif
 
c          go back to the minimization routine.
         goto 111
 
      endif
 
c           ---------- the end of the loop -------------
 
c     If task is neither FG nor NEW_X we terminate execution.
 
      if (json_active) then
         call json_write_aggregate(trim(lbfgsb_json), task, f,
     +                             dsave(13), n, x)
      endif
 
      stop
 
      end
 
c======================= The end of driver3 ============================