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X 2. X 4. X 3. X 1. X 5. STA107 Lecture 25 Markov Chain Probabilities. tomorrow. today. yesterday & past. Markov Property: The state of the system at time t +1 depends only on the state of the system at time t. Time Homogeneous Property:
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X2 X4 X3 X1 X5 STA107 Lecture 25Markov Chain Probabilities tomorrow today yesterday & past Markov Property: The state of the system at time t+1 depends only on the state of the system at time t
Time Homogeneous Property: Transition probabilities are independent of time (t) Example • Weather: • raining today 40% rain tomorrow • 60% no rain tomorrow • not raining today 20% rain tomorrow • 80% no rain tomorrow
0.6 0.4 0.8 rain no rain 0.2 Transition matrix • Stochastic matrix: • Rows sum up to 1 • Rows are conditional mass functions
p p p p 0 1 99 2 100 Start (10$) 1-p 1-p 1-p 1-p Markov ProcessGambler’s Example • – Gambler starts with $10 • - At each play we have one of the following: • • Gambler wins $1 with probabilityp • • Gambler looses $1 with probability 1-p • – Game ends when gambler goes broke, or gains a fortune of $100 • (Both 0 and 100 are absorbing states)
p p p p 0 1 99 2 100 Start (10$) 1-p 1-p 1-p 1-p Markov Process • Markov process - described by graph • Markov chain - a random walk on this graph (distribution over paths) • One step transition matrix gives