How Does Fortran Generate 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

 

[LudusRex]

I can provide some insight into Fortran's random numbers. First, it's important to understand that computers are deterministic machines, meaning they follow a set of instructions and produce the same results every time they are given the same input. This applies to random number generation as well.

Fortran uses a pseudo-random number generator (PRNG) to generate random numbers. This means that the numbers are not truly random, but they are generated using a mathematical algorithm that produces a sequence of numbers that appear to be random. The PRNG uses a starting value called a seed, and from this seed, it generates a sequence of numbers that may seem random but are actually predetermined.

The reason why the numbers don't change each time you run the program is because the PRNG uses the same seed value by default. If you want to generate a different sequence of numbers, you can change the seed value before running the program.

So, are the numbers really random? It depends on your definition of randomness. While they are not truly random in the sense that they are predetermined, the sequence of numbers generated by the PRNG can still be considered random for most practical purposes.

In conclusion, Fortran's random numbers are generated using a pseudo-random number generator, which produces a sequence of numbers that may appear random but are actually predetermined. By changing the seed value, you can generate different sequences of numbers.