There is a requirement that I need to generate 10 groups of random numbers. The dimension of each group of random numbers is 5*5. It is required that each group of random numbers is different, but it is also required that the random numbers generated each time the program is run are repeatable.

The simplest way is as follows:

program test_random_number
  !!!!!!You can not set seeds, and the effect is the same.
  REAL :: r(5,5)
  do i=1,10
  call random_number(r)
  write(*,*)r
  print*,'-------------------------------------'
  enddo
end program

After the program runs, the output result is:

 

 3.9208680E-07  2.5480442E-02  0.3525161      0.6669145      0.9630555    
  0.8382882      0.3353550      0.9153272      0.7958636      0.8326931    
  0.3450427      0.8711839      8.9918353E-02  0.8882838      0.7009789    
  0.7345526      0.3001758      4.9717721E-02  0.9081894      9.7658597E-02
  4.0313378E-02  8.5024789E-02  0.5588210      0.9264517      7.5640768E-02
 -------------------------------------
  0.9117896      9.1822170E-02  0.6377664      0.8522921      0.1210777    
  0.9945745      0.7782503      1.9665021E-02  0.1698636      0.9947433    
  0.7536924      0.2179738      0.6592925      0.5390184      0.4800633    
  0.8392264      2.5420204E-02  0.9893829      0.5857707      0.7670679    
  0.4448168      0.7095050      0.7945260      0.4387013      0.2087533    
 -------------------------------------
  0.7311121      0.6657310      0.7220742      0.2114710      0.3082515    
  0.2629889      0.7522959      0.5497946      0.6367239      0.6310104    
  0.4947841      0.4706950      0.1225150      0.5348967      0.1941571    
  0.9679053      0.5892302      1.7623320E-02  0.3143427      0.5533030    
  0.6762834      1.6883278E-02  0.2656559      0.4608800      0.8374500    
 -------------------------------------

The output of each run is the same.

I think the above results are because fortran has a random seed by default, so it is not set to call random directly_ Number is OK.

If you want to be more flexible, instead of using the default random seed, you can manually set a random seed as follows:

program test_random_number
  !!!!!!Set a seed. Each run will generate the same random number, but the random number generated in each cycle is different
  !!!!!!The effect is the same as not seeding.
  REAL :: r(5,5)
  integer :: n(1)
  integer,allocatable :: seed(:)
  n=123456
  call random_seed(put=n)
  
  print*,'-------------------------------------'
  do i=1,10
  call random_number(r)
  write(*,*)r
  print*,'-------------------------------------'
  enddo


end program

N is the seed we set, and put is random_ The input parameter (intent(in)) of the seed subroutine, n must be an array. About random_ The other two parameters of seed, size and get, are output parameters. The author doesn't understand them very well and doesn't need to use them. You are welcome to comment in the comment area. Personally, I think this article is pretty good: fortran random number

The output results are as follows:

 0.3003711      6.1110102E-02  3.7764840E-02  0.2076357      0.3833852    
  0.9097154      0.4229082      0.2671735      0.5746257      0.2194885    
  0.5764998      0.3967984      2.7026536E-02  0.3349927      0.3099868    
  0.5780981      0.9329451      0.6820918      0.7257171      0.6534119    
  0.9531794      0.5080327      0.8002245      0.4509397      0.9372804    
 -------------------------------------
  0.5612365      6.1461501E-02  0.7858571      0.5554050      0.4812418    
  0.6018271      0.3862819      0.7944903      3.1226246E-02  0.5575908    
  0.5348483      0.3856399      0.6524287      0.8872858      5.1918231E-02
  3.9682582E-02  7.7522576E-02  0.8136503      0.8178805      0.4109471    
  0.6253451      0.3680272      0.9016623      0.3865243      0.3946394    
 -------------------------------------
  0.7769522      0.9103879      0.4235442      0.8339527      0.2920198    
  0.7666448      4.0062513E-02  0.2423317      0.8170069      0.4758632    
  0.4376644      0.8842280      0.2314132      0.9875546      0.8472762    
  0.8744933      0.8001316      2.4753891E-02  0.6369917      3.1933367E-02
  0.5903373      0.9698811      0.5209839      0.1557297      0.5503737    
 -------------------------------------

It can be seen that different from the random number generated when no random seed is set, the result of each run is the same, and another random number can be obtained by changing the assignment of n.

In addition, if you want to make the random number obtained by running the program different each time (the program running result will not be repeatable), you can write as follows:

program test_random_number
  REAL :: r(5,5)
  call random_seed()
  do i=1,10
  call random_number(r)
  write(*,*)r
  print*,'-------------------------------------'
  enddo
end program

That is, call random_seed(), but no parameters are passed in. Random seeds are set according to the system time each time. The more specific principle is mentioned in the link just now.

fortran sets random seeds and generates random numbers. The above meets the author's needs. If there is a more high-end usage, please leave a message in the comment area.