/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 81 (a) Let \(\\{N(t), t \geqslant 0... [FREE SOLUTION] | 91影视

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(a) Let \(\\{N(t), t \geqslant 0\\}\) be a nonhomogeneous Poisson process with mean value function \(m(t) .\) Given \(N(t)=n\), show that the unordered set of arrival times has the same distribution as \(n\) independent and identically distributed random variables having distribution function $$ F(x)=\left\\{\begin{array}{ll} \frac{m(x)}{m(t)}, & x \leqslant t \\ 1, & x \geqslant t \end{array}\right. $$ (b) Suppose that workmen incur accidents in accordance with a nonhomogeneous Poisson process with mean value function \(m(t) .\) Suppose further that each injured man is out of work for a random amount of time having distribution \(F\). Let \(X(t)\) be the number of workers who are out of work at time \(t .\) By using part (a), find \(E[X(t)]\).

Short Answer

Expert verified
In summary, the unordered set of arrival times for nonhomogeneous Poisson process with mean value function \(m(t)\) has the same distribution as \(n\) independent and identically distributed random variables with distribution function \(F(x)=\frac{m(x)}{m(t)}, x \leqslant t\), and \(F(x)=1, x \geqslant t\). The expected number of workers who are out of work at time \(t\) is given by \(E[X(t)] = \sum_{i=1}^{N(t)} \int_0^t \frac{m(t_i)}{m(t)} f_{T_i}(t_i) dt_i\).

Step by step solution

01

Define notation

Let \(T_1, T_2, ..., T_n\) denote the unordered set of arrival times and \(X_1, X_2, ..., X_n\) be the \(n\) independent and identically distributed random variables with distribution function \(F(x)\).
02

Calculate joint probability density function

To show that the unordered set of arrival times has the same distribution as \(n\) independent and identically distributed random variables, we need to find the joint probability density function (pdf) of \(T_1, T_2, ..., T_n\) given that \(N(t) = n\). Using the definition of the nonhomogeneous Poisson process, the joint pdf of the arrival times can be written as: $$ f_{T_1, T_2,...,T_n}(t_1, t_2,...,t_n) = \frac{1}{n!} m^n(t) e^{-m(t)} $$ Here, \(m^n(t)\) represents the nth power of the function \(m(t)\) and \(m(t)\) is the mean value function of the process.
03

Determine the distribution function for the arrival times

Now we need to find the distribution function of \(T_i\) for \(i = 1,2,\dots ,n\). Differentiate the joint pdf with respect to \(t_i\): $$ f_{T_i}(t_i) = \frac{\partial^n f_{T_1, T_2,...,T_n}(t_1, t_2,...,t_n)}{\partial t_1 \partial t_2 \dots \partial t_n} \Big|_{t_1 = t_2 = \dots = t_n = t_i} $$ However, since our goal is to show that this distribution is equal to the given \(F(x)\), we need to find the cumulative distribution function (CDF) of \(T_i\) and compare it with the given \(F(x)\). The CDF of \(T_i\) is given by: $$ F_{T_i}(x) = P(T_i \leqslant x) = \int_0^x f_{T_i}(t_i) dt_i $$
04

Calculate the CDF and compare with the given distribution

By integrating the pdf \(f_{T_i}(t_i)\) from Step 3, we can calculate the CDF \(F_{T_i}(x)\): $$ F_{T_i}(x)= \left\{ \begin{array}{ll} \int_0^x \frac{1}{n!} m^n(t) e^{-m(t)} dt_i = \frac{m(x)}{m(t)}, & x \leqslant t \\ 1, & x \geqslant t \end{array} \right. $$ This confirms that the unordered set of arrival times \(T_1, T_2, ..., T_n\) has the same distribution as the \(n\) independent and identically distributed random variables with distribution function \(F(x)\).
05

Find the expected value of \(X(t)\)

Using the result from part (a), we can calculate the expected value of \(X(t)\), the number of workers who are out of work at time \(t\). The expected value of \(X(t)\) is given by: $$ E[X(t)] = E[\sum_{i=1}^{N(t)} F(T_i)] $$ Now, taking the expectation inside the sum, we get: $$ E[X(t)] = \sum_{i=1}^{N(t)} E[F(T_i)] = \sum_{i=1}^{N(t)} \int_0^t F(T_i) f_{T_i}(t_i) dt_i \\ $$ Using the CDF \(F_{T_i}(x)\) from Step 4, we can calculate its expectation: $$ E[X(t)] = \sum_{i=1}^{N(t)} \int_0^t \frac{m(t_i)}{m(t)} f_{T_i}(t_i) dt_i $$ This is the expected number of workers who are out of work at time \(t\) considering that workmen incur accidents in accordance with a nonhomogeneous Poisson process with mean value function \(m(t)\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Mean Value Function
The mean value function is a crucial concept in understanding nonhomogeneous Poisson processes, which describe events that do not occur uniformly over time. Unlike the homogeneous Poisson process, which has a constant rate, the rate of occurrence in a nonhomogeneous Poisson process changes over time.

The mean value function, generally denoted as \( m(t) \), indicates the expected number of events occurring by time \( t \). It essentially provides a running total of the average number of events as time progresses. Mathematical definition aside, you can think of it much like a car's odometer reading over time, where the reading at any given time reflects the cumulative distance traveled.

In the context of the exercise, the function \( m(t) \) is critical because it helps to define the expected pattern of events, or in our practical application, the distribution of workers' accidents over time.
Random Variables
A random variable is a foundational pillar of probability theory. Essentially, it is a variable whose possible values are numerical outcomes of a random phenomenon. There are two types of random variables: discrete, which can take on a countable number of values, and continuous, which can take on an infinite number of values within an interval.

In the given exercise, the random variables represent the arrival times of events in the process, specifically the times at which workers incur accidents. These random variables have specific properties鈥攖hey鈥檙e independent, meaning the occurrence of one event doesn't affect the likelihood of another, and identically distributed, where each event shares the same probability distribution.
Probability Density Function
When dealing with continuous random variables, the probability density function (pdf) is an indispensable tool. It describes the relative likelihood for this random variable to take on a given value. The pdf helps to compute probabilities for continuous random variables by integrating over intervals.

In the step-by-step solution, we find the joint probability density function for the arrival times of events. This function essentially gives us a landscape of probabilities across different times, showing how densely packed the events are likely to be over the timeline of our process. The concept of a joint pdf is a bit more intricate, as it deals with multiple variables and their collective behavior.
Cumulative Distribution Function
The cumulative distribution function (CDF) can be seen as a companion to the pdf; it is a function that tells us the probability that a random variable is less than or equal to a certain value. It ramps up from 0 to 1 as you move from left to right along the number line, reflecting the accumulating odds of your random variable falling within that range.

In this exercise, we compared the CDF of the arrival times to a given distribution function to show equivalency. This step is a pivotal one鈥攊t鈥檚 the 鈥渁ha moment鈥 where we confirm that the distribution of workers' accident times behaves according to the prescribed distribution function \( F(x) \).
Expected Value
The expected value, denoted as \( E[X] \), is what we predict on average from a random variable \( X \). It's found by summing up all possible values of \( X \), each weighted by its probability. For a continuous variable, this summing is an integral over the range of the variable.

In the context of the exercise, we were tasked with finding the expected number of workers out of work at a particular time \( t \). This expected value, \( E[X(t)] \), translates into a practical forecast that can guide staffing decisions or insurance estimates in a real-world scenario. By integrating the previously found CDF against the density function, we derived this expected value, bringing together the concepts we explored to deliver a tangible output.

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Most popular questions from this chapter

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