Markov Models - 20 August 2011 - BioInformatics Pakistan
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Markov Models


Markov Models

1. Description:
   In probability theory, a Markov model is a stochastic model that assumes the Markov property. Generally, this assumption enables reasoning and computation with the model that would otherwise be intractable.

2. Key Points:

 1. Set of states: 
 2. Process moves from one state to another generating a sequence of states :
 
 3. Markov chain property:  probability of each subsequent state depends only on what was the previous state:
 4. To define Markov model, the following probabilities have to be specified: transition probabilities
and initial probabilities

3. Example of Markov Model:

  1. Two states : ‘Rain’ and ‘Dry’.
  2. Transition probabilities: P(‘Rain’|‘Rain’)=0.3 , P(‘Dry’|‘Rain’)=0.7 , P(‘Rain’|‘Dry’)=0.2, P(‘Dry’|‘Dry’)=0.8
  3. Initial probabilities: say P(‘Rain’)=0.4 , P(‘Dry’)=0.6 .

4. Calculation of sequence probability
  1. By Markov chain property, probability of state sequence can be found by the formula:
  2. Suppose we want to calculate a probability of a sequence of states in our example, {‘Dry’,’Dry’,’Rain’,Rain’}. P({‘Dry’,’Dry’,’Rain’,Rain’} ) = P(‘Rain’|’Rain’) P(‘Rain’|’Dry’) P(‘Dry’|’Dry’) P(‘Dry’)= 0.3*0.2*0.8*0.6



Category: Algorithms | Views: 516 | Added by: Ansari | Rating: 0.0/0
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