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In [[probability theory]], a '''nearly completely decomposable (NCD) Markov chain''' is a [[Markov chain]] where the state-space can be partitioned in such a way that movement within a partition occurs much more frequently that movement between partitions.<ref>{{cite jstor|1427937}}</ref> Particularly efficient algorithms exist to compute the [[stationary distribution]] of Markov chains with this property.<ref name="kms">{{cite doi|10.1137/0605019}}</ref> | |||
==Definition== | |||
[[Albert Ando|Ando]] and [[Franklin M. Fisher|Fisher]] define a completely decomposable matrix as one where "an identical rearrangement of rows and columns leaves a set of square [[submatrices]] on the [[principal diagonal]] and zeros everywhere else." A nearly completely decomposable matrix is one where an identical rearrangement of rows and columns leaves a set of square submatrices on the principal diagonal and ''small nonzeros'' everywhere else.<ref>{{cite doi|10.2307.2F2525455}}</ref><ref>{{cite jstor|1913078}}</ref> | |||
==Example== | |||
A [[Markov chain]] with [[transition matrix]] | |||
::<math>P = | |||
\begin{pmatrix} | |||
\frac{1}{2} & \frac{1}{2} & 0 & 0 \\ | |||
\frac{1}{2} & \frac{1}{2} & 0 & 0 \\ | |||
0 & 0 & \frac{1}{2} & \frac{1}{2} \\ | |||
0 & 0 & \frac{1}{2} & \frac{1}{2} \\ | |||
\end{pmatrix} + \epsilon \begin{pmatrix} | |||
-\frac{1}{2} & 0 & \frac{1}{2} & 0 \\ | |||
0 & -\frac{1}{2} & 0 & \frac{1}{2} \\ | |||
\frac{1}{2} & 0 & -\frac{1}{2} & 0 \\ | |||
0 & \frac{1}{2} & 0 & -\frac{1}{2} \\ | |||
\end{pmatrix}</math> | |||
is nearly completely decomposable if ''ε'' is small (say 0.1).<ref>Example 1.1 from {{cite book|page=8|title=Discrete-time Markov chains: two-time-scale methods and applications|first1=George|last1=Yin|first2=Qing|last2=Zhang|publisher=Springer|year=2005|isbn= 0-387-21948-X}}</ref> | |||
==Stationary distribution algorithms== | |||
Special-purpose iterative algorithms have been designed for NCD Markov chains<ref name="kms" /> though the multi–level algorithm, a general purpose algorithm,<ref>{{cite doi|10.1145/183019.183040}}</ref> has been shown experimentally to be competitive and in some cases significantly faster.<ref>{{cite techreport|title=On the Utility of the Multi-Level Algorithm for the Solution of Nearly Completely Decomposable Markov Chains (ICASE Report No. 94-44)|url=http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA284423|last1=Leutenegger |first1=Scott T.|last2=Horton |first2=Graham |month=June | year=1994 |quote=We present experimental results indicating that the general- purpose Multi-Level algorithm is competitive, and can be significantly faster than the special-purpose KMS algorithm when Gauss-Seidel and Gaussian Elimination are used for solving the individual blocks. Markov chains, Multi- level, Numerical solution.|institution=NASA|id=Contractor Report 194929}}</ref> | |||
==See also== | |||
* [[Lumpability]] | |||
==References== | |||
{{Reflist}} | |||
[[Category:Markov processes]] | |||
{{Probability-stub}} |
Revision as of 07:59, 13 January 2013
In probability theory, a nearly completely decomposable (NCD) Markov chain is a Markov chain where the state-space can be partitioned in such a way that movement within a partition occurs much more frequently that movement between partitions.[1] Particularly efficient algorithms exist to compute the stationary distribution of Markov chains with this property.[2]
Definition
Ando and Fisher define a completely decomposable matrix as one where "an identical rearrangement of rows and columns leaves a set of square submatrices on the principal diagonal and zeros everywhere else." A nearly completely decomposable matrix is one where an identical rearrangement of rows and columns leaves a set of square submatrices on the principal diagonal and small nonzeros everywhere else.[3][4]
Example
A Markov chain with transition matrix
is nearly completely decomposable if ε is small (say 0.1).[5]
Stationary distribution algorithms
Special-purpose iterative algorithms have been designed for NCD Markov chains[2] though the multi–level algorithm, a general purpose algorithm,[6] has been shown experimentally to be competitive and in some cases significantly faster.[7]
See also
References
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- ↑ 2.0 2.1 Template:Cite doi
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- ↑ Example 1.1 from 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 - ↑ Template:Cite doi
- ↑ Template:Cite techreport