On Tuesday 23 July 2002 20:54, Todd Miller wrote:
Eric Maryniak wrote:
... That should not, however, discourage you from writing a new and improved random number package for numarray.
Yes, thank you :-)
... 3. I wonder what the design philosophy is behind the decision to use 'mathematically suspect' seeding as default behavior.
Using time for a seed is fairly common. Since it's an implementation detail, I doubt anyone would object if you can suggest a better default seed.
Well, as said, a fixed seed, provided by the class implementation and therefore 'good', instead of a not-so-random 'random' seed. And imho it would be better not to (only) use the clock, but a /dev/random kinda thing. Personally, I find the RNG setup much more appealing: there the default is: standard_generator = CreateGenerator(-1) where seed < 0 ==> Use the default initial seed value. seed = 0 ==> Set a "random" value for the seed from the system clock. seed > 0 ==> Set seed directly (32 bits only). And indeed 'void Mixranf(int *s,u32 s48[2])' uses a built-in constant as initial seed value (actually, two).
...
If you use default seed()'ing now and re-run your program/model later with identical parameters, you will get different output.
When you care about this, you need to set the seed to something deterministic.
Naturally, but how do I know what a 'good' seed is (or indeed it's type, range, etc.)? I just would like, as e.g. RNG does, let the number generator take care of this... (or at least provide the option to)
...
In the programs I've seen so far, including a lot of ours ahem, usually a program (simulation) is run multiple times with the same parameters and, in our case for neural nets, seeded each time with a clock generated seed and then the different simulations are compared and checked if they are similar or sensitive to chaotic influences. But I don't think this is the proper way to do this. My point is, I guess, that the sequence of these clock-generated seeds itself is not random, because (as for RandomArray) the generated numbers are clearly not random. Better, and reproducible, would be to start the first simulation with a supplied seed, get the seed and pickle after the first run and use the pickled seed for run 2 etc. or indeed have a kind of master script (as you suggest) that manages this. That way you would start with one seed only and are not re-seeding for each run. Because if the clock-seeds are not truly random, you will a much greater change of cycles in your overall sequence of numbers. Bye-bye, Eric -- Eric Maryniak <e.maryniak@pobox.com> WWW homepage: http://pobox.com/~e.maryniak/ Mobile phone: +31 6 52047532, or (06) 520 475 32 in NL. VME ERROR 37022: Hierarchic name syntax invalid taking into account starting points defined by initial context.