HW4

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Des Moines Area Community College *

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330

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Statistics

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Apr 3, 2024

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docx

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8

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1. Classify each of the following stochastic processes as discrete-time or continuous-time, and discrete-space or continuous-space. (a) The temperature in downtown Ames throughout the day The temperature is continuous-state and any time throughout the day is continuous-time (b) The high temperature in downtown Ames for each day in a year The temperature is continuous-state and each day is discrete-time (c) The number of customers in line at Café B throughout the day The number of customers is discrete-state and any time throughout the day is continuous-time (d) The total number of customers served each day at Café B The total number of customers served is discrete-state and each day is discrete-time (e) The operational state, denoted 1 or 0, of a certain machine recorded at the end of each hour The operational state is discrete-state and the end of each hour is discrete-time 2. A certain machine used in a manufacturing process can be in one of three states: Fully operational (“full"), partially operational (“part"), or broken (“broken"). If the machine is fully operational today, there is a 0.7 probability it will be fully operational again tomorrow, a 0.2 chance it will be partially operational tomorrow, and otherwise tomorrow it will be broken. If the machine is partially operational today, there is a 0.6 probability it will continue to be partially operational tomorrow and otherwise it will be broken (because the machine is never repaired in its partially operational state). Finally, if the machine is broken today, there is a 0.8 probability it will be repaired to fully operational status tomorrow; otherwise, it remains broken. Let X = the state of the machine on day n. (a) Identify the state space of this chain. State space ={F, P, B} ( F: full, P: part, B: broken} (b) Determine the one-step transition probability matrix. P FF = 0.7, P FP = 0.2, P FB = 1 – 0.7 – 0.2 = 0.1 P PF = 0 , P PP = 0.6, P PB = 1 - 0.6 = 0.4 P BF = 0.8, P BP = 0, P BB = 1 – 0.8 = 0.2 1-step Transition Probability Matrix
P = 0.7 0.2 0.1 0 0.6 0.4 0.8 0 0.2 (c) Given the machine is broken today, find the probability that it will stay broken the day after tomorrow. P = P BF * P FB + P BB * P BB = 0.8 * 0.1 + 0.2 * 0.2 = 0.12 Alternate calculations P 0 = (0,0,1) P 2 = P 0 * P * P = (0,0,1) * 0.7 0.2 0.1 0 0.6 0.4 0.8 0 0.2 * 0.7 0.2 0.1 0 0.6 0.4 0.8 0 0.2 = (0.8, 0, 0.2) * 0.7 0.2 0.1 0 0.6 0.4 0.8 0 0.2 = (0.72, 0.16, 0.12) => Probability it will stay broken the day after tomorrow is 0.12 3. Information bits (0s and 1s) in a binary communication system travel through a long series of relays. At each relay, a “bit-switching" error might occur. Suppose that at each relay, there is a 4% chance of a 0 bit being switched to a 1 bit and a 5% chance of a 1 becoming a 0. Let X 0 = a bit’s initial parity (0 or 1), and let Xn = the bit’s parity after traversing the n th relay. (a) Construct the one-step transition matrix for this chain. [Hint: There are only two states, 0 and 1.] P 00 = 1- 0.04 = 0.96, P 01 = 0.04 P 10 = 0.05, P 11 = 1 -0.05 = 0.95 1-step transition matrix P = 0.96 0.04 0.05 0.95 (b) Suppose the input stream to this relay system consists of 80% 0s and 20% 1s. Determine the proportions of 0s and 1s exiting the first relay. P 0 = (0.8,0.2) P 1 = P 0 * P = (0.8,0.2) * ( 0.96 0.04 0.05 0.95 ) = (0.778, 0.222) => 77.8% 0s and 22.2% 1s (c) Under the same conditions as the last part, determine the proportions of 0s and 1s exiting the third relay
P 2 = P 0 * P * P = (0.778, 0.222) * ( 0.96 0.04 0.05 0.95 ) = (0.75798, 0.24202) P 3 = P 0 * P * P * P = (0.75798, 0.24202) * ( 0.96 0.04 0.05 0.95 ) = (0.7398, 0.2602) 73.98% 0s and 26.02% 1s 4. A hamster is placed into the three-chambered circular habitat shown in the figure below. Sitting in any chamber, the hamster is equally likely to next visit either of the two adjacent chambers. Let Xn = the nth chamber visited by the hamster. (a) Construct the one-step transition matrix for this Markov chain. P 11 = 0, P 12 = 0.5, P 13 = 0.5 P 21 = 0.5, P 22 = 0, P 23 = 0.5 P 31 = 0.5, P 32 = 0.5, P 33 = 0 1-step transition matrix P = 0 0.5 0.5 0.5 0 0.5 0.5 0.5 0 (b) Is this a regular Markov chain? [Hint: Look at the 2-step transition matrix] A Markov Chain {Xt} with transition matrix P is said to be regular if, for some n, all entries of P (n) are positive (> 0). P 2 = 0 0.5 0.5 0.5 0 0.5 0.5 0.5 0 * 0 0.5 0.5 0.5 0 0.5 0.5 0.5 0 = 0.5 0.25 0.25 0.25 0.5 0.25 0.25 0.25 0.5 All entries of P 2 are positive => regular Markov (c) Find the steady-state probabilities of this chain.
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