Fortran's Random numbers

[michela02]

Fortran's Random numbers!

Hi everyone!
I have a doubt about random numbers on Fortran: how does the computer choose random numbers? Why don't they change each time I run the programme? Are they really random then?
Thanks!

 

[gsal]

randomness in itself is a complicated matter...I think you need to read up on it.

I don't know much about randomness, all I can tell is that I can imagine different algorithms are probably designed to generate a series of random numbers, where the randomness has to do with the fact that the numbers do not follow a certain pattern or sequence or something...now, because it is an algorithm that generates the numbers, there is a repeatability in the process, the process is started with what is called a seed...whenever you start with the same seed, the sequence of numbers is going to be the same...again, that does not mean that it is not a random sequence...got it? the randomnes is in the non-pattern of the sequence.

 

[Borek]

They are pseudorandom, most likely prepared using linear congruential generator. You should be able to modify the seed (which will make the sequence different each time).

 

[Niles]

If you need a very large amount of random numbers, then it may be beneficial to use the Mersenne twister: http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/VERSIONS/FORTRAN/fortran.html