Re: easy question about random numbers

*To*: mathgroup at smc.vnet.net*Subject*: [mg53391] Re: easy question about random numbers*From*: "Steve Luttrell" <steve_usenet at _removemefirst_luttrell.org.uk>*Date*: Sun, 9 Jan 2005 23:03:44 -0500 (EST)*References*: <crqb7f$cak$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

You could use MultinomialDistribution. Here is an example: <<Statistics`MultiDiscreteDistributions` k = 10; p = (#1/Total[#1] & )[Table[Random[], {k}]]; n = 1; dist = MultinomialDistribution[n, p]; k is the number of states, p is the vector of state probabilities (in this case these are random numbers that sum to unity), and n is the number of trials. You can then use Random[dist] to generate a histogram with k bins, and with the n trials placed in the appropriate bins. In this case (i.e. n=1) there is a 1 in one of the bins, and the rest of the bins contain 0. If you use RandomArray[dist, m] you can generate the result of m evaluations of Random[dist]. Alternatively, if you don't mind lumping all of the results together in a single histogram (this wipes out knowledge of the order in which the trials occurred) you could set n = m in the first place, and then evaluate Random[dist] once. Here is how this works for n = 100: k = 10; p = (#1/Total[#1] & )[Table[Random[], {k}]]; n = 100; dist = MultinomialDistribution[n, p]; Random[dist] Steve Luttrell "Pedrito" <pedrito6 at softhome.net> wrote in message news:crqb7f$cak$1 at smc.vnet.net... > Hi everybody! > > I wanted to obtain a discrete random number generator that I needed for > a project. > > On the library Statistics`DiscreteDistributions` I could find the > DiscreteUniformDistribution > function. But I wanted to specify the probability for each one of the > states. > > > For instance: > If we need to simulate an unfair dice, we could have this probabilities > for each one of the sides: > {1/6, 1/6, 1/6, 1/6, 9/60, 11/60} > > So I wrote: > li2 = {1/6, 1/6, 1/6, 1/6, 9/60, 11/60} > li3=FoldList[Plus,0,li2] > Module[{i = 1, r = Random[]}, While[ !li3[[i]] < r < li3[[i + 1]], i++]; > i] > > It works ok but I don't know if there is another (better) way of doing > this. > Any suggestion? >