About the pseudo random generator in gfortran

[ch l]

Hi,

I'm a ordinary user of The GNU Fortran Compiler. I'm still trying my best
to learn the Fortran programming language. When I am using The GNU Fortran
Compiler, I try to use the internal pseudo random generator like this:

call random_seed()
call random_number(rnd)

This code is quite common on many Fortran textbook or on many websites. The
2nd line might also be use in a DO loop. Although I compile and run it for
many times, I get totally SAME random number(s). I have tested the same
code on Intel 's Fortran Compiler, Intel 's Fortran Compiler will give
different number for the every time I run it.

I have tried this both on Windows (MinGW, TDM-GCC) and directly on Linux's
original GCC. They seem to have same problem. I also tried to search on
Google, but there seems no useful answer.

I have read the official wiki, the example in the function RANDOM_NUMBER
(which URL is https://gcc.gnu.org/onlinedocs/gfortran/RANDOM_005fNUMBER.html
) use a new SUBRUTINE named init_random_seed, and its define is in the
RANDOM_SEED page (
https://gcc.gnu.org/onlinedocs/gfortran/RANDOM_005fSEED.html#RANDOM_005fSEED).
So I have tried the init_random_seed subroutine in my own code, it seems
works well, I get the different number for every times I run the program.

But I'm really confused that why GNU's Fortran Compiler requires a external
subroutine to generate random number. So I wonder if this is a bug or it
is just designed to behave like this. It will be better if you can teach me
a lot. Maybe there is a more elegant way to generate random number. ;)

I'm very sorry to disturb you, but I hope you can reply to me soon. Thanks
a lot.

Best regards,
lch