Re: Re: populate a list with random numbers from normal distribution?

*To*: mathgroup at smc.vnet.net*Subject*: [mg49969] Re: [mg49963] Re: [mg49855] populate a list with random numbers from normal distribution?*From*: DrBob <drbob at bigfoot.com>*Date*: Sun, 8 Aug 2004 05:37:56 -0400 (EDT)*References*: <200408070752.DAA07857@smc.vnet.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

Look up RandomArray in Help, and use the built-in distributions. Bobby On Sat, 7 Aug 2004 03:52:33 -0400 (EDT), sean_incali <sean_incali01 at yahoo.com> wrote: > Hi. > > I hate it when i ask a question and not sound clear. I'm sure it's > frustrating for those who are really making efforts to help me out. > > let me try this. > > > --- Tomas Garza <tgarza01 at prodigy.net.mx> wrote: > >> Sean, >> Back to first principles: the normal distribution is a continuous >> distribution. Hence, a list of whatever integers can't possibly come >> from a >> normal distribution. > > > Right. I understand this now due to you and many others who tirelessly > pointed out my errors. (bless them all, lol) > > >> Sampling from a normal distribution will produce >> integers only with probability zero. You may, of course, define any >> distribution which will produce integers in the range you desire. >> E.g., a >> discrete uniform distribution which assigns probability 1/90000 to >> each >> integer in the range {10000,99999}, or any other distribution. >> Sampling from >> this distribution once and again will have a constant mean and >> variance. > > Yes this is kinda what i wanted. Only reason I wanted to use the > integers is because of the issues raised previously, and because i > didn't understand them fully. > > I wanted to pick the integers from a distribution in a range and then > scale the integers to make real numbers. > > You said the discrete uniform distribution will pick intergers in the > range {10000,99999}, or any other distribution. > > Will it do normal or poissonian distribution in that range? if so how > do I implement that? > > > >> Did >> I understand your problem correctly? >> > > I believe so. > > To add more information if it will help... > > I'm basically doing a perturbation analysis where i'm making random > perturbation to certain inputs into a system. and I woudl like to have > statistical information about the perturbation. (such as variance and > standard deviation and mean) > > then once I have perturbed the system, i would like to take an > output(s) and do the same statistical analysis to see what the system > did. > > which is why it was important to generate same variance and the mean > consistently because i will be performign this over and over. (if i > change the mean, std dev, and variance of inputs then the output will > be different also) > > I hope i have made my questions more understandable. > > thanks much in advance > > sean > >> Tomas >> ----- Original Message ----- >> From: "sean kim" <sean_incali at yahoo.com> To: mathgroup at smc.vnet.net > To: mathgroup at smc.vnet.net >> To: "Tomas Garza" <tgarza01 at prodigy.net.mx> >> Cc: <mathgroup at smc.vnet.net> >> Sent: Thursday, August 05, 2004 12:15 AM >> Subject: [mg49969] [mg49963] Re: [mg49855] populate a list with random numbers >> fromnormaldistribution? >> >> >> > Hi tomas >> > >> > What I wanted to do is to pick sets of random Integers >> > in the ranges {10000, 99999} from the Normal >> > distribution such that, the mean is 50000 and the >> > standard deviation is 25000. >> > >> > or is that not normal distribution? will that be a >> > custom distribution? >> > >> > if that isn't possible, then I want to pick set of >> > random intgers ranging from {10000, 99999} such that >> > the variance and the mean and standard deviation do >> > not change across different runs. >> > >> > I think i'm supposed to use SeedRandom here but this >> > caused me problems also. >> > >> > so I need to design a routine that will pick random >> > integers in a given range with a given distribution >> > with the SAME mean, std dev/ and variances across >> > different runs or simulations. >> > >> > any insights will be truly appreciated. >> > >> > >> > sean >> > >> > >> > >> > > > l1 = Table[Random[NormalDistribution[50000,25000], >> > > Integer, {10000, 99999}], {1000}]; >> > >> > --- Tomas Garza <tgarza01 at prodigy.net.mx> wrote: >> > >> > > Check your syntax. Look at the following: >> > > >> > > In[1]:= >> > > << "Statistics`" >> > > >> > > In[2]:= >> > > dist = NormalDistribution[50000, 25000]; >> > > >> > > In[4]:= >> > > Table[Random[dist], {10}] >> > > Out[4]= >> > > {26975.950556122647, 58550.03432245862, >> > > 90456.47272543506, 73888.28476391576, >> > > 52046.50992913155, 72675.80052590193, >> > > 48593.27989475152, 78918.83089186646, >> > > 96303.52480806905, 69543.82643195332} >> > > >> > > What, then, do you mean by the variance of the above >> > > table? >> > > >> > > Tomas Garza >> > > Mexico City >> > > ----- Original Message ----- >> > > From: "sean kim" <sean_incali at yahoo.com> To: mathgroup at smc.vnet.net > To: mathgroup at smc.vnet.net >> > > To: <mathgroup at smc.vnet.net> >> > > Sent: Wednesday, August 04, 2004 9:46 AM >> > > Subject: [mg49969] [mg49963] [mg49855] populate a list with random >> > > numbers from normal >> > > distribution? >> > > >> > > >> > > > hello group. >> > > > >> > > > I looked at the help browser but i can't figure >> > > this out. I weant to >> > > > make a list of random numbers sampled from a >> > > normal distribution >> > > > >> > > > In[90]:= >> > > Needs["Statistics`ContinuousDistributions`"] >> > > > >> > > > l1 = Table[Random[NormalDistribution[50000,25000], >> > > Integer, {10000, >> > > > 99999}], {1000}]; >> > > > >> > > > Variance[l1]//N >> > > > StandardDeviation[l1]//N >> > > > >> > > > >> > > > From In[90]:= >> > > > Random::"randt": >> > > > Type specification NormalDistribution[50000, >> > > 25000] in >> > > > <<1>> should be Real, Integer, or Complex. >> > > > >> > > > Out[92]= >> > > > 0. >> > > > Out[93]= >> > > > 0. >> > > > >> > > > thanks in advance for any insights >> > > > >> > > > sean >> > > > >> > > > >> > > >> > > >> > > >> > >> > >> > >> > >> > >> > >> > __________________________________ >> > Do you Yahoo!? >> > Y! Messenger - Communicate in real time. Download now. >> > http://messenger.yahoo.com >> > >> >> >> > > > > > __________________________________ > Do you Yahoo!? > Yahoo! Mail - 50x more storage than other providers! > http://promotions.yahoo.com/new_mail > > > -- DrBob at bigfoot.com www.eclecticdreams.net

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