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)
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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.
>
>
>
>