Hi, For getting reproducible results, setting the random number generator seed in the beginning from the global random number generator is a good way to do it as long as you are not using non-monotonic propagators. The rationale for using an LCG as the standard random number generator in Gecode is that it is simple, fast, gives decent random numbers, and it has a small state.
However, please note that just using random variable and value selection will not give you a random solution with any kind of known distribution. Finding random solutions to CSPs with a given (usually uniform) distribution is a non-trivial problem. IMHO, XorSample by Gomes, Sabharwal, and Selman [1] is a nice example of how to get near-uniform solutions to SAT-problems. Cheers, Mikael [1] http://www.cs.cornell.edu/~sabhar/publications/xorSamplingNIPS06.pdf On Mon, May 18, 2009 at 7:01 PM, Martin Mann <mm...@informatik.uni-freiburg.de> wrote: > > Alright, what is my scenario: > > I have a stochastic simulation e.g. a Markov chain. Within this > simulation, for each step x_i a CSP is formulated and I would like to > get a random solution r. This solution r is accepted based on some > probability. Thus, I can stay at x_i (x_(i+1)=x_i) or proceed to r > (x_(i+1)=r). > > So I have two "areas" where random numbers are produced: (1) the Markov > chain and (2) the randomized branching within Gecode. > > Now I would like to have ONE pseudo random number generator (RNG) used > for both to ensure that I have reproducable results... > > One possible hack is the following: > - assume RNG_M for the markov chain and RNG_G for gecode internals. > - for each step I set the seed of RNG_G via a random number drawn from RNG_M > - I use RNG_M for the Markov chain step check > > Would be an option, but it would ease the problem a lot if one could > directly use the same RNG for both or not? > > Another point about arbitrary RNGs is about statistics. I am working in > a field were e.g. physics care a lot about the random number > distributions and statistics a pseudo random number generator gives. > Therefore, these people like to set up their favorite RNG they trust > most to give low-biased stochastic simulations. > In the above solution, the RNG_M can be defined freely, the RNG_G not. > > That's why I was asking. :) It's not about speed or space, more about > application. > > But so long the above solution will do or has to be sufficient. > > Thanks, > > Martin > > > > > Javier Andrés Mena Zapata schrieb: >> Hi, >> >> Just curiosity... Do you prefer RNG speed, RNG space, general speed or >> general space? >> >> Cheers, >> >> On Mon, May 18, 2009 at 2:55 AM, Mikael Zayenz Lagerkvist >> <zay...@gmail.com>wrote: >> >>> Hi, >>> >>> Currently it is not possible to exchange the random number generator. >>> Furthermore, the implementation uses properties of the random number >>> generator that would most probably compromise efficiency if they were >>> abstracted away (for example, the state is limited to a single >>> unsigned int as seed). If you want to use your own random number >>> generator, I would suggest writing your own subclasses of ViewSelBase >>> and ValSelbase similar to ViewSelRnd and ValRnd. >>> >>> For curiosity, what is the reason that you want to change the random >>> number generator used? >>> >>> Cheers, >>> Mikael >>> >>> On Sat, May 16, 2009 at 12:37 AM, Martin Mann >>> <mm...@informatik.uni-freiburg.de> wrote: >>>> Hi everybody, >>>> >>>> I digged a bit into the Gecode source about the randomized branching >>>> supported since version 3. >>>> >>>> In line 124 in gecode/support/random.hpp I found the definition of >>>> RandomGenerator internally used in the view selection: >>>> >>>> >>> http://www.gecode.org/doc-latest/reference/group__FuncSupport.html#g02fe942f90a57a25639f09960dab4459 >>>> As given there, it is just a typedef onto the >>>> LinearCongruentialGenerator provided by Gecode but I would like to set >>>> up my own random number generator... >>>> >>>> Is there a possibility to support user defined generators? e.g. in >>>> coming versions? >>>> >>>> If not available right now, maybe you like the following suggestion: >>>> >>>> A possibility would be a super class 'RNG' that has to be implemented by >>>> every generator plus a kind of factory class 'RNF' with static members >>> only. >>>> The RNF would be a wrapper around the current RNG instance to use >>>> (stored in a static internal member). Thus, all Gecode internals that >>>> need a random number use a static interface of RNF instead of some RNG >>>> instance members. So the library gets independent of the concrete RNG >>>> used and you get the possibility to register a user defined RNG within >>>> the RNF. Per default the RNF can use the linear congruential generator >>>> provided. The static interface and data member would avoid annoying >>>> copies of RNGs all around and won't complicate your Gecode >>> internals/source. >>>> >>>> Just a suggestion... if it is already possible just ignore and please >>>> let me know how to do with the current Gecode version. :) >>>> >>>> >>>> Have a nice weekend, >>>> >>>> Martin >>>> >>>> >>>> _______________________________________________ >>>> Gecode users mailing list >>>> us...@gecode.org >>>> https://www.gecode.org/mailman/listinfo/gecode-users >>>> >>> >>> >>> -- >>> Mikael Zayenz Lagerkvist, >>> http://www.ict.kth.se/~zayenz/<http://www.ict.kth.se/%7Ezayenz/> >>> >>> _______________________________________________ >>> Gecode users mailing list >>> us...@gecode.org >>> https://www.gecode.org/mailman/listinfo/gecode-users >>> >> >> >> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> Gecode users mailing list >> us...@gecode.org >> https://www.gecode.org/mailman/listinfo/gecode-users > > -- > Martin Mann, Dipl. Bioinf. > Bioinformatics - Inst. of Computer Science > Albert-Ludwigs-University Freiburg > Tel: ++49-761-203-8259 > Fax: ++49-761-203-7462 > http://www.bioinf.uni-freiburg.de/~mmann/ > > _______________________________________________ > Gecode users mailing list > us...@gecode.org > https://www.gecode.org/mailman/listinfo/gecode-users > -- Mikael Zayenz Lagerkvist, http://www.ict.kth.se/~zayenz/ _______________________________________________ Gecode users mailing list us...@gecode.org https://www.gecode.org/mailman/listinfo/gecode-users
