Random seed initialization

[Angelo Graziosi]

Ciao Janus,

Il 06/04/2013 17.03, Janus Weil ha scritto:
>
>>
>> I have tested this on Cygwin with its GCC-4.5.3 packages,
>>
>> $ gfortran -v
>> Using built-in specs.
>> COLLECT_GCC=gfortran
>> COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-pc-cygwin/4.5.3/lto-wrapper.exe
>> Target: i686-pc-cygwin
>> Configured with:
>> /gnu/gcc/releases/respins/4.5.3-3/gcc4-4.5.3-3/src/gcc-4.5.3/configure
>> --srcdir=/gnu/gcc/releases/respins/4.5.3-3/gcc4-4.5.3-3/src/gcc-4.5.3
>> --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin
>> --libexecdir=/usr/lib --datadir=/usr/share --localstatedir=/var
>> --sysconfdir=/etc --datarootdir=/usr/share --docdir=/usr/share/doc/gcc4 -C
>> --datadir=/usr/share --infodir=/usr/share/info --mandir=/usr/share/man -v
>> --with-gmp=/usr --with-mpfr=/usr --enable-bootstrap
>> --enable-version-specific-runtime-libs --libexecdir=/usr/lib --enable-static
>> --enable-shared --enable-shared-libgcc --disable-__cxa_atexit --with-gnu-ld
>> --with-gnu-as --with-dwarf2 --disable-sjlj-exceptions
>> --enable-languages=ada,c,c++,fortran,java,lto,objc,obj-c++ --enable-graphite
>> --enable-lto --enable-java-awt=gtk --disable-symvers --enable-libjava
>> --program-suffix=-4 --enable-libgomp --enable-libssp --enable-libada
>> --enable-threads=posix --with-arch=i686 --with-tune=generic
>> --enable-libgcj-sublibs CC=gcc-4 CXX=g++-4 CC_FOR_TARGET=gcc-4
>> CXX_FOR_TARGET=g++-4 GNATMAKE_FOR_TARGET=gnatmake
>> GNATBIND_FOR_TARGET=gnatbind --with-ecj-jar=/usr/share/java/ecj.jar
>> Thread model: posix
>> gcc version 4.5.3 (GCC)
>>
>> and with a my build of 4.9.0 20130324,
>>
>> $ gfortran-4.9 -v
>> Using built-in specs.
>> COLLECT_GCC=gfortran-4.9
>> COLLECT_LTO_WRAPPER=/usr/local/gfortran/libexec/gcc/i686-pc-cygwin/4.9.0/lto-wrapper.exe
>> Target: i686-pc-cygwin
>> Configured with: /home/angelo/work/gcc-4.9-20130324/configure
>> --prefix=/usr/local/gfortran --program-suffix=-4.9
>> --enable-languages=c,c++,fortran --enable-checking=release
>> --enable-threads=posix --enable-libgomp --with-arch=native
>> --with-tune=native --with-fpmath=sse --disable-bootstrap
>> --disable-libmudflap --disable-shared
>> Thread model: posix
>> gcc version 4.9.0 20130324 (experimental) (GCC)
>>
>>
>> I suspect this behavior is to be expected for a snapshot...
>
> Not really!
>
> [...]
>
> Maybe you could post the output of this enhanced version (which also
> prints the clock and seed values):
>
> program rnd_init
>    implicit none
>    real :: rnd(9)
>    call init_random_seed()
>    call random_number(rnd)
>    print *,"random: ",rnd
> contains
>    SUBROUTINE init_random_seed()
>      INTEGER :: i, n, clock
>      INTEGER, DIMENSION(:), ALLOCATABLE :: seed
>
>      CALL RANDOM_SEED(size = n)
>      print *,"n=",n
>      ALLOCATE(seed(n))
>
>      CALL SYSTEM_CLOCK(COUNT=clock)
>      print *,"clock:", clock
>      seed = clock + 37 * (/ (i - 1, i = 1, n) /)
>      CALL RANDOM_SEED(PUT = seed)
>      print *,"seed: ",seed
>      DEALLOCATE(seed)
>    END SUBROUTINE init_random_seed
> end program rnd_init
>

When I compile it with GCC-4.5.3 the results are:

$ ./rnd_init.out  !! 1st run
  n=           8
  clock:  1609234520
  seed:   1609234520  1609234557  1609234594  1609234631  1609234668 
1609234705  1609234742  1609234779
  random:   0.20771700      0.70008731      5.39250970E-02  0.93139762 
     0.64063454      0.79792714      0.44434732      0.53217107 
0.92274189

$ ./rnd_init.out  !! 2nd run
  n=           8
  clock:  1609240114
  seed:   1609240114  1609240151  1609240188  1609240225  1609240262 
1609240299  1609240336  1609240373
  random:   0.21628165      0.50345588      0.47903579      0.87107950 
     0.64046717      0.82357150      0.49985659      0.13067204 
0.22462136

$ ./rnd_init.out  !! 3rd run
  n=           8
  clock:  1609245348
  seed:   1609245348  1609245385  1609245422  1609245459  1609245496 
1609245533  1609245570  1609245607
  random:   0.71807641      0.52906609      5.59192896E-03  0.52994502 
     0.36918062      0.28023791      8.55535269E-03  0.15218848 
0.52063912

etc..

Using my build of GCC-4.9.0 20130324, each run produces always this

$ ./rnd_init.out
  n=          12
  clock:           0
  seed:            0          37          74         111         148 
      185         222         259         296         333         370 
       407
  random:   0.301754534      0.380439878      0.926293135 
0.672118008      0.237815678      0.638214409      0.320253670 
0.351599574      0.865273237

It seems the call to SYSTEM_CLOCK() is failing..

>
> Might be a platform-specific problem (with SYSTEM_CLOCK?!?) ...

... or my build of GCC is not so good (see above for configure options)...


Ciao,
  Angelo.