i'm guilty of screwing up my cut and paste -- they were from different machines. the mystery was real. i just showed the wrong output.
the problem was that i set the seed variable and didn't call srand. i was making all sorts of mistakes yesterday. that's what you get when you work 10 hours straight without taking a break. :( pete begin Matt Holland <[EMAIL PROTECTED]> > Jeff Newmiller wrote: > > >The random driver may be used to obtain a seed for random() or rand(), or > >it could be used to obtain random numbers on its own. You run a risk of > >extracting all of the randomness from the system if you depend on random > >for long random sequences, though, and a /dev/random that has run out of > >entropy is a file that will block until that condition changes. > > > >Having known psuedo-random sequences does allow you to "repeat" > >monte-carlo simulations. To answer Peter, yes, rand() is supposed to be > >deterministic for this very reason. I am puzzled by the same issue Ken is > >puzzled by, though... failing to call srand() should always cause rand() > >to yield the same pseudo-random sequence... it should never have yielded > >variable results in the first place! > > > I don't think there's any mystery here. If you compare the two sets of > runs (late in the day vs. early in the day), you will see that the early > runs have "trials: 1000000", whereas the later runs have "trials: 1000". > I'm assuming that "trials" is some parameter that probably influences > the number of random numbers generated within a simulation, so you > wouldn't expect the same answer even with the same seed, since a > parameter has been changed. > > Matt > > > > > > >>On Tuesday 02 April 2002 06:26 pm, you wrote: > >> > >>>>Date: Tue, 2 Apr 2002 14:47:20 -0800 > >>>>[CODE SNIPPED] > >>>> > >>>So this is when the program is seeded to /dev/random: > >>> > >>>> p@satan% ./ising2-jfunc 4.0 > >>>> T: 4.0e+00 beta: 2.500e-01 trials: 1000 N: 10 M: 10 seed: > >>>>3497451914 Average Energy: -1.273893 > >>>> Average magnetization: 0.425220 > >>>> Average |magnetization|: 0.531100 > >>>> Average magnetic susceptibility: 34.746600 > >>>> > >>>And this is when the code is seeded to 1: > >>> > >>>> T: 4.0e+00 beta: 2.500e-01 trials: 1000 N: 10 M: 10 seed: > >>>>3497451914 Average Energy: -1.326747 > >>>> Average magnetization: 0.495320 > >>>> Average |magnetization|: 0.495320 > >>>> Average magnetic susceptibility: 28.645040 > >>>> > >>>And you've established that if you run it repeatedly you keep getting > >>>the > >>same thing: > >> > >>>> T: 4.0e+00 beta: 2.500e-01 trials: 1000 N: 10 M: 10 seed: > >>>>3497451914 Average Energy: -1.326747 > >>>> Average magnetization: 0.495320 > >>>> Average |magnetization|: 0.495320 > >>>> Average magnetic susceptibility: 28.645040 > >>>> > >>>BUT four hours earlier: > >>> > >>>>Date: Tue, 2 Apr 2002 10:05:34 -0800 > >>>> > >>>This is when you seed it to /dev/random: > >>> > >>>> T: 4.0e+00 beta: 2.500e-01 trials: 1000000 > >>>> N: 10 M: 10 seed: 208006379 > >>>> Average Energy: -1.057143 > >>>> Average magnetization: 0.002008 > >>>> Average |magnetization|: 0.251765 > >>>> Average magnetic susceptibility: 8.948655 > >>>> > >>>And this is when you seed it to 1: > >>> > >>>> T: 4.0e+00 beta: 2.500e-01 trials: 1000000 > >>>> N: 10 M: 10 seed: 208006379 > >>>> Average Energy: -1.050182 > >>>> Average magnetization: 0.030723 > >>>> Average |magnetization|: 0.246092 > >>>> Average magnetic susceptibility: 8.692724 > >>>> > >>>Why did 4 hours of time change the results when you seed it to 1 ??? > >>>_______________________________________________ > >>>vox-tech mailing list > >>>[EMAIL PROTECTED] > >>>http://lists.lugod.org/mailman/listinfo/vox-tech > >>> > >>_______________________________________________ > >>vox-tech mailing list > >>[EMAIL PROTECTED] > >>http://lists.lugod.org/mailman/listinfo/vox-tech > >> > >> > > > >--------------------------------------------------------------------------- > >Jeff Newmiller The ..... ..... Go Live... > >DCN:<[EMAIL PROTECTED]> Basics: ##.#. ##.#. Live Go... > > Live: OO#.. Dead: OO#.. Playing > >Research Engineer (Solar/Batteries O.O#. #.O#. with > >/Software/Embedded Controllers) .OO#. .OO#. rocks...2k > >--------------------------------------------------------------------------- > > > > > >_______________________________________________ > >vox-tech mailing list > >[EMAIL PROTECTED] > >http://lists.lugod.org/mailman/listinfo/vox-tech > > > > > > _______________________________________________ > vox-tech mailing list > [EMAIL PROTECTED] > http://lists.lugod.org/mailman/listinfo/vox-tech _______________________________________________ vox-tech mailing list [EMAIL PROTECTED] http://lists.lugod.org/mailman/listinfo/vox-tech
