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PGI Fortran 中的随机数生成器不是那么随机

转载 作者:行者123 更新时间:2023-12-01 13:47:32 25 4
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下面的代码只是生成了一个简单的随机数三元组:

program testrand

integer, parameter :: nz = 160, nf = 160, nlt = 90

real :: tmpidx(3)
integer :: idxarr(3), idx1, idx2, idx3, seed_size, ticks
integer, allocatable :: seed(:)

call random_seed(size=seed_size)
allocate(seed(seed_size))

call system_clock(count=ticks)
seed = ticks+37*(/(i-1, i=1,seed_size)/)
call random_seed(put=seed)

deallocate(seed)

call random_number(tmpidx)
idxarr = tmpidx * (/nz, nf, nlt/)
idx1 = max(1,idxarr(1))
idx2 = max(1,idxarr(2))
idx3 = max(1,idxarr(3))
print *,idx1, idx2, idx3

end program

我用 gfortran 编译它并运行几次,我得到:

> gfortran testrand.f90
> ./a.out
74 98 86
> ./a.out
113 3 10
> ./a.out
44 104 27

看起来很随意。现在我用 PGI Fortran 编译并运行几次:

> pgf90 testrand.f90
> ./a.out
1 1 1
> ./a.out
1 1 1
> ./a.out
1 1 1

当然,没有办法完全确定,但我怀疑这不是随机的。 :) 有人知道这里发生了什么吗?有人知道使用 PGI Fortran 获取随机数的正确方法吗?

最佳答案

不知何故,PGI 不像 GNU 编译器那样实现 system_clock。我不知道为什么,我最近通过像你一样做类似的事情发现了它。

要了解我在说什么,只需在调用 system_clock 后打印 ticks。使用 PGI 时,您可能总是得到 0,而使用 GNU 编译器时,可能会得到不同的数字。要解决您的问题,您可以修改以下代码。它是代码的略微修改版本,您可以在 GNU fortran web site 获得

program testrand
use iso_fortran_env, only: int64

integer, parameter :: nz = 160, nf = 160, nlt = 90
real :: tmpidx(3)
integer :: idxarr(3), idx1, idx2, idx3, seed_size, ticks
integer, allocatable :: seed(:)

call random_seed(size=seed_size)
allocate(seed(seed_size))

! call system_clock(count=ticks)
! seed = ticks+37*(/(i-1, i=1,seed_size)/)
! call random_seed(put=seed)
!
! deallocate(seed)

call init_random_seed()

call random_number(tmpidx)
idxarr = tmpidx * (/nz, nf, nlt/)
idx1 = max(1,idxarr(1))
idx2 = max(1,idxarr(2))
idx3 = max(1,idxarr(3))
print *,idx1, idx2, idx3

contains
!
subroutine init_random_seed()
implicit none
integer, allocatable :: seed(:)
integer :: i, n, istat, dt(8), pid
integer(int64) :: t

integer, parameter :: un=703

call random_seed(size = n)
allocate(seed(n))
! First try if the OS provides a random number generator
open(unit=un, file="/dev/urandom", access="stream", &
form="unformatted", action="read", status="old", iostat=istat)
if (istat == 0) then
read(un) seed
close(un)
else
! The PID is
! useful in case one launches multiple instances of the same
! program in parallel.
call system_clock(t)
if (t == 0) then
call date_and_time(values=dt)
t = (dt(1) - 1970) * 365_int64 * 24 * 60 * 60 * 1000 &
+ dt(2) * 31_int64 * 24 * 60 * 60 * 1000 &
+ dt(3) * 24_int64 * 60 * 60 * 1000 &
+ dt(5) * 60 * 60 * 1000 &
+ dt(6) * 60 * 1000 + dt(7) * 1000 &
+ dt(8)
end if
pid = getpid()
t = ieor( t, int(pid, kind(t)) )
do i = 1, n
seed(i) = lcg(t)
end do
end if
call random_seed(put=seed)
!print*, "optimal seed = ", seed
end subroutine init_random_seed
!
function lcg(s)
integer :: lcg
integer(int64), intent(in out) :: s
if (s == 0) then
s = 104729
else
s = mod(s, 4294967296_int64)
end if
s = mod(s * 279470273_int64, 4294967291_int64)
lcg = int(mod(s, int(huge(0), 8)), kind(0))
end function lcg
!
!this option is especially used for pgf90 to provide a getpid() function
!> @brief Returns the process ID of the current process
!! @todo write the actual code, for now returns a fixed value
!<
function getpid()result(pid)
integer pid
pid = 53 !just a prime number, no special meaning
end function getpid
end program

关于PGI Fortran 中的随机数生成器不是那么随机,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/34797938/

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