program MaxAllocate
! This file: http://ftp.aset.psu.edu/pub/ger/fortran/hdk/dynmax.f90
!
!=== Example of Allocating a 1D DP Array as large as possible (to about
!    the nearest MB DP elements) on the platform running this code.

      integer :: AllocStatus, DeallocStatus, MB
      integer(kind=selected_int_kind(18)) :: na  ! for > 2GB
      real(kind(1.D0)), allocatable, dimension(:) :: a

        MB=1024**2   ! Allocate to nearest Megabyte.
!---Kind=DP array assumed to have 8-byte elements.
        na=0         ! na is a test amount to allocate.
        do
          na=na+MB
          allocate( a(na), stat=AllocStatus)
          if (AllocStatus  /= 0) then
            na=na-MB ! When no more heap storage is availabe, quit.
            exit
          else
            deallocate(a,stat=DeallocStatus)
            ! if this Allocate worked, deallocate and iterate.
            if (DeallocStatus /= 0) then
              print *, "Could not Deallocate??"
              stop
            endif
          endif
        end do

        allocate( a(na))
          print *, "Size of DP allocated array is: ",na
          print *, "Size of the allocated array is: ",(na*8)/MB,"MB"
          a(na)=0   ! Test the allocated array.
        deallocate(a)

! When run this on our 64-bit Linux cluster, which allows one to utilize
! up to 32GB, the above program, when compiled using the Intel Fortran
! compiler (v9.1), or the PathScale compiler (v2.3) displays the
! followig results:
!
! Hammer:
! Size of DP allocated array is:    4073717760
! Size of the allocated array is:   31080 MB
!
! Unisys3:
! Size of DP allocated array is:    16131293184
! Size of the allocated array is:   123072 MB
!

 end program