# Spacing of the results of Fortran intrinsic random\_number

**URL:** <https://fortran-lang.discourse.group/t/spacing-of-the-results-of-fortran-intrinsic-random-number/10884>\
**Category:** Uncategorized\
**Created:** [May 2, 2026, 12:36pm UTC](https://fortran-lang.discourse.group/t/spacing-of-the-results-of-fortran-intrinsic-random-number/10884 "2026-05-02T12:36:22Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![JohnCampbell](https://avatars.discourse-cdn.com/v4/letter/j/5daacb/32.png) [@JohnCampbell](https://fortran-lang.discourse.group/u/JohnCampbell)\
**Post date:** [May 3, 2026, 12:56am UTC](https://fortran-lang.discourse.group/t/spacing-of-the-results-of-fortran-intrinsic-random-number/10884/3 "2026-05-03T00:56:52Z")

</div>

Here is a simple test of random\_number using two Fortran compilers I use.  
These tests indicate:  
The returned value is in the range ( 0 \<= random\_number(x) \< 1 )  
Silverfrost FTN95 is a reproduceable sequence, while  
Gfortran 15.1.0 uses a different starting value ( for the compile options I used)

For my Monte-Carlo simulations I mostly used a reproduceable sequence.

```auto
    implicit none
    integer :: n,k,i
    real*4 :: x, mi_x, ma_x

    open (unit=11, file='random.log', position='append')
    
    write (11,*) 'Vern : ',compiler_version ()
    write (11,*) 'Opts : ',compiler_options ()

    n = 2  
    mi_x = 1
    ma_x = 0
    do k = 1,24
      do i = 1,n
        call random_number (x)
        if ( x == 0. ) write (11,*) 'zero detected', i
        if ( x == 1. ) write (11,*) 'one detected', i
        if ( x > ma_x ) ma_x = x
        if ( x < mi_x ) mi_x = x
      end do
      write (11,fmt='(i8,2g18.8)') n,mi_x, ma_x
      n = n*2
    end do

    end

```

```auto
 Vern : FTN95 v9.20
 Opts : 64;CHECKMATE;ECHO_OPTIONS;ERROR_NUMBERS;IMPLICIT_NONE;INTL;LINK;LOGL;NO_BANNER;UNLIMITED_ERRORS;VS7;
       2 0.33098495 0.67307037
       4 0.89860201E-01 0.74144781
       8 0.55308938E-02 0.75059688
      16 0.55308938E-02 0.93005449
      32 0.55308938E-02 0.98703653
      64 0.55308938E-02 0.98703653
     128 0.55308938E-02 0.99690789
     256 0.11609793E-02 0.99690789
     512 0.10038018E-02 0.99690789
    1024 0.78243017E-03 0.99844843
    2048 0.78243017E-03 0.99930221
    4096 0.16486645E-03 0.99948233
    8192 0.69141388E-04 0.99998528
   16384 0.28550625E-04 0.99998528
   32768 0.97155571E-05 0.99998528
   65536 0.35762787E-05 0.99999893
  131072 0.35762787E-05 0.99999893
  262144 0.35762787E-05 0.99999952
  524288 0.11920929E-06 0.99999952
 1048576 0.11920929E-06 0.99999952
 2097152 0.11920929E-06 0.99999958
 4194304 0.11920929E-06 0.99999970
 zero detected 7634751
 8388608 0.0000000 0.99999988
 zero detected 2906636
16777216 0.0000000 0.99999994
 Vern : GCC version 15.1.0
 Opts : -cpp -iprefix C:/Program Files (x86)/gcc_eq/gcc_15.1.0/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/ -U_REENTRANT -mtune=generic -march=x86-64 -fno-underscoring -fdollar-ok
       2 0.48348904E-02 0.69568729    
       4 0.48348904E-02 0.79884946    
       8 0.48348904E-02 0.85110766    
      16 0.59008598E-04 0.92572713    
      32 0.59008598E-04 0.95438445    
      64 0.59008598E-04 0.99653119    
     128 0.59008598E-04 0.99690586    
     256 0.59008598E-04 0.99839717    
     512 0.59008598E-04 0.99957311    
    1024 0.59008598E-04 0.99957311    
    2048 0.59008598E-04 0.99957311    
    4096 0.59008598E-04 0.99957311    
    8192 0.55015087E-04 0.99961603    
   16384 0.30994415E-05 0.99991792    
   32768 0.30994415E-05 0.99993944    
   65536 0.30994415E-05 0.99999046    
  131072 0.16093254E-05 0.99999100    
  262144 0.16093254E-05 0.99999577    
  524288 0.16093254E-05 0.99999577    
 1048576 0.95367432E-06 0.99999845    
 2097152 0.59604645E-06 0.99999887    
 zero detected 3443890
 4194304 0.0000000 0.99999952    
 8388608 0.0000000 0.99999994    
 zero detected 811674
 zero detected 4808671
16777216 0.0000000 0.99999994    
 Vern : FTN95 v9.20
 Opts : 64;CHECKMATE;ECHO_OPTIONS;ERROR_NUMBERS;IMPLICIT_NONE;INTL;LINK;LOGL;NO_BANNER;UNLIMITED_ERRORS;VS7;
       2 0.33098495 0.67307037
       4 0.89860201E-01 0.74144781
       8 0.55308938E-02 0.75059688
      16 0.55308938E-02 0.93005449
      32 0.55308938E-02 0.98703653
      64 0.55308938E-02 0.98703653
     128 0.55308938E-02 0.99690789
     256 0.11609793E-02 0.99690789
     512 0.10038018E-02 0.99690789
    1024 0.78243017E-03 0.99844843
    2048 0.78243017E-03 0.99930221
    4096 0.16486645E-03 0.99948233
    8192 0.69141388E-04 0.99998528
   16384 0.28550625E-04 0.99998528
   32768 0.97155571E-05 0.99998528
   65536 0.35762787E-05 0.99999893
  131072 0.35762787E-05 0.99999893
  262144 0.35762787E-05 0.99999952
  524288 0.11920929E-06 0.99999952
 1048576 0.11920929E-06 0.99999952
 2097152 0.11920929E-06 0.99999958
 4194304 0.11920929E-06 0.99999970
 zero detected 7634751
 8388608 0.0000000 0.99999988
 zero detected 2906636
16777216 0.0000000 0.99999994
 Vern : GCC version 15.1.0
 Opts : -cpp -iprefix C:/Program Files (x86)/gcc_eq/gcc_15.1.0/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/ -U_REENTRANT -mtune=generic -march=x86-64 -fno-underscoring -fdollar-ok
       2 0.67090213E-01 0.50203764    
       4 0.40025771E-01 0.96130651    
       8 0.11717677E-01 0.96130651    
      16 0.11717677E-01 0.96130651    
      32 0.11717677E-01 0.99553567    
      64 0.11436999E-01 0.99949199    
     128 0.55414438E-02 0.99949199    
     256 0.34532547E-02 0.99949199    
     512 0.21323562E-02 0.99949199    
    1024 0.45263767E-03 0.99949199    
    2048 0.40495396E-03 0.99982810    
    4096 0.33193827E-03 0.99982810    
    8192 0.63836575E-04 0.99998480    
   16384 0.39398670E-04 0.99998719    
   32768 0.14841557E-04 0.99999207    
   65536 0.71525574E-05 0.99999207    
  131072 0.11920929E-06 0.99999797    
  262144 0.11920929E-06 0.99999797    
  524288 0.11920929E-06 0.99999964    
 zero detected 859344
 1048576 0.0000000 0.99999964    
 2097152 0.0000000 0.99999964    
 4194304 0.0000000 0.99999982    
 8388608 0.0000000 0.99999994    
 zero detected 3340268
16777216 0.0000000 0.99999994

```

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