Re: Bug with ProbabilityDistribution

*To*: mathgroup at smc.vnet.net*Subject*: [mg132548] Re: Bug with ProbabilityDistribution*From*: Barrie Stokes <barrie.stokes at newcastle.edu.au>*Date*: Thu, 10 Apr 2014 03:09:38 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net

Hi Charles Writing scriptD = ProbabilityDistribution[ Piecewise[{{0, x1 == 1 && x2 == 1}, {1/2, x1 == 1 && x2 == 0}, {0, x1 == 0 && x2 == 1}, {1/2, x1 == 0 && x2 == 0}}], {x1, 0, 1, 1}, {x2, 0, 1, 1} ], PDF[ scriptD, {x, y}] looks interesting, and CDF[ scriptD, {x, y}] gives Undefined. OTOH, Mean[scriptD ] gives (1=8E2, 0) And Variance[scriptD ] gives {1=8E4, 0} whereas Covariance[scriptD ] doesn't work. DiscretePlot3D[ PDF[ scriptD, {x, y}], {x, -2, 2}, {y, -2, 2}, AxesLabel -> {"x", "y", "PDF"} ] Corroborates PDF[ scriptD, {1, 1}] PDF[ scriptD, {0, 1}] PDF[ scriptD, {1, 0}] PDF[ scriptD, {0, 0}] If you look closely. I note that there is documentation in V.9 for Discrete Univariate Distributions, but I don't see anything under "Discrete Multivariate Distributions" Hmmm. Cheers Barrie On 9/04/14 6:14 PM, "CHARLES GILLINGHAM" <cgillingham1 at me.com> wrote: >Evaluate this: > > ProbabilityDistribution[ > Piecewise[{{0, x1 == 1 && x2 == 1}, {1/2, x1 == 1 && x2 == 0}, {0, x1 >== 0 && x2 == 1}, {1/2, x1 == 0 && x2 == 0}}], > {x1, 0, 1, 1}, {x2, 0, 1, 1} > ] > PDF[%][{1, 1}] > >And you get: > > Undefined > >But the probability is obviously 0 > >Is there something I am misunderstanding about how simple Boolean >probability distributions should be set up? > >Thanks. > > > >