Chapter 3: Problem 4
Let \(P=\left[\begin{array}{cc}0.5 & 0.3 \\ 0.5 & 0.7\end{array}\right]\) be the transition matrix for a Markov chain with two states. Let \(\mathbf{x}_{0}=\left[\begin{array}{l}0.5 \\ 0.5\end{array}\right] b e\) the initial state vector for the population. Find the steady state vector.
Short Answer
Expert verified
The steady state vector is \( \begin{bmatrix} \frac{3}{8} \\ \frac{5}{8} \end{bmatrix} \)."
Step by step solution
01
Understand the Steady State Condition
A steady state vector \( \mathbf{x} \) for a Markov chain's transition matrix \( P \) satisfies the equation \( P \mathbf{x} = \mathbf{x} \). This means that once the system reaches the steady state, it does not change in subsequent transitions.
02
Set Up the Steady State Equation
For the given transition matrix \( P = \begin{bmatrix} 0.5 & 0.3 \ 0.5 & 0.7 \end{bmatrix} \) and steady state vector \( \mathbf{x} = \begin{bmatrix} x_1 \ x_2 \end{bmatrix} \), the equation becomes: \[ \begin{bmatrix} 0.5 & 0.3 \ 0.5 & 0.7 \end{bmatrix} \begin{bmatrix} x_1 \ x_2 \end{bmatrix} = \begin{bmatrix} x_1 \ x_2 \end{bmatrix}. \] This results in a system of linear equations.
03
Write the System of Equations
Multiply the matrix \( P \) by \( \mathbf{x} \) to get the system:\[ 0.5x_1 + 0.3x_2 = x_1 \]\[ 0.5x_1 + 0.7x_2 = x_2 \].
04
Simplify and Solve the System
Rearrange the equations from Step 3:1. \( 0.5x_1 + 0.3x_2 = x_1 \) simplifies to \( 0.5x_1 = 0.3x_2 \) or \( x_1 = 0.6x_2 \).2. \( 0.5x_1 + 0.7x_2 = x_2 \) simplifies to \( 0.5x_1 = 0.3x_2 \), which is consistent as it is same.Introduce the condition \( x_1 + x_2 = 1 \) for the steady state vector and solve: \( x_1 = 0.6x_2 \) gives \( 0.6x_2 + x_2 = 1 \) resulting in \( 1.6x_2 = 1 \), therefore \( x_2 = \frac{5}{8} \) and \( x_1 = \frac{3}{8} \).
05
Verify the Solution
Ensure that your solution satisfies the requirement of all probabilities summing to 1:\( x_1 + x_2 = \frac{3}{8} + \frac{5}{8} = 1 \). Thus, the steady state vector is \( \begin{bmatrix} \frac{3}{8} \ \frac{5}{8} \end{bmatrix} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Transition Matrix
A transition matrix is a square matrix used in Markov chains, where each entry represents the probability of transitioning from one state to another. For the given example:
- The matrix is given by \[ P = \begin{bmatrix} 0.5 & 0.3 \ 0.5 & 0.7 \end{bmatrix} \].
- Each column must sum to 1, ensuring that all possible outcomes are accounted for in each state transition.
- Here, the system consists of two states, and the numbers within the matrix specify the probability of transitioning from one state to another.
Steady State
A steady state is a condition where the probabilities remain constant over time despite further transitions. In other words:
- The system no longer changes as transitions occur, implying a sort of "equilibrium" in the chain.
- To find this steady state, you solve the equation \[ P \mathbf{x} = \mathbf{x} \].
- In our example, after solving the steady-state equation, we find the vector \[ \mathbf{x} = \begin{bmatrix} \frac{3}{8} \ \frac{5}{8} \end{bmatrix} \].
Linear Equations
Linear equations form the backbone of solving for the steady state in a Markov chain. The goal is to set up and solve these equations based on the transition matrix. Here's how it works:
- Consider the matrix multiplication, \[ \begin{bmatrix} 0.5 & 0.3 \ 0.5 & 0.7 \end{bmatrix} \begin{bmatrix} x_1 \ x_2 \end{bmatrix} = \begin{bmatrix} x_1 \ x_2 \end{bmatrix} \], which yields a system of linear equations.
- These equations are:\[ 0.5x_1 + 0.3x_2 = x_1 \] \[ 0.5x_1 + 0.7x_2 = x_2 \].
- Simplifying these equations allows us to express one variable in terms of the other, leading to easy substitution and solving.
Probability Vector
A probability vector is a vector whose components represent probabilities, which sum to 1. This concept is essential when dealing with Markov chains.
- The vector \( \mathbf{x}_0 \) represents the initial state probabilities as \[ \begin{bmatrix} 0.5 \ 0.5 \end{bmatrix} \].
- In context, each entry reflects the likelihood of the system being in a particular state.
- As the Markov chain evolves, this vector changes in accordance with the transition matrix until it converges to a steady state vector.
- For the steady state, we ensure our derived vector, \[ \begin{bmatrix} \frac{3}{8} \ \frac{5}{8} \end{bmatrix} \], meets the requirement that all elements of a probability vector must add up to 1.