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Investigate the behavior of the discrete logistic equation $$ x_{t+1}=R_{0} x_{t}\left(1-x_{t}\right) $$ Compute \(x_{t}\) for \(t=0,1,2, \ldots, 20\) for the given values of \(r\) and \(x_{0}\), and graph \(x_{t}\) as a function of \(t .\) \(R_{0}=3.1, x_{0}=0.9\)

Short Answer

Expert verified
Iteratively calculate \(x_t\) using the logistic equation for each step from \(t=0\) to \(t=20\), then plot \(x_t\) against \(t\).

Step by step solution

01

Understand the discrete logistic equation

The given equation \(x_{t+1} = R_{0} x_{t}(1-x_{t})\) defines a sequence of values for \(x_t\) over discrete time steps \(t\). Here, \(R_0\) is the growth rate parameter, and \(x_0\) is the initial value at \(t=0\).
02

Set initial conditions

Use the initial condition \(x_0 = 0.9\). This is the starting value for the sequence, and we will use it to calculate subsequent values of \(x_t\).
03

Compute \(x_1\)

To find \(x_1\), substitute \(x_0 = 0.9\) and \(R_0 = 3.1\) into the equation:\[x_{1} = 3.1 \cdot 0.9 \cdot (1 - 0.9) = 3.1 \cdot 0.9 \cdot 0.1 = 0.279\]
04

Compute subsequent values

Continue using the equation \(x_{t+1} = R_{0} x_{t}(1-x_{t})\) to calculate \(x_2, x_3, \ldots, x_{20}\) iteratively. For instance:\[x_{2} = 3.1 \cdot 0.279 \cdot (1 - 0.279) \approx 0.622719\]
05

Repeat calculations until \(t=20\)

Repeat the calculations as described in Step 4 for each time step up to \(t=20\).
06

Graph \(x_t\) versus \(t\)

After computing the values of \(x_t\) for each time \(t\), plot these values on a graph with \(t\) on the x-axis and \(x_t\) on the y-axis to observe the behavior of the sequence.

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Key Concepts

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

Iterative Calculations
Iterative calculations involve repeating a set of mathematical operations over and over, using the result from one step as the input for the next. In the context of the discrete logistic equation, iterative calculations allow us to find the sequence of values for \(x_t\) for each time step \(t\).

Here’s how it works in this exercise:
  • The initial value, \(x_0\), is given, which is \(0.9\) in this case.
  • The equation used is \(x_{t+1} = 3.1 \, x_t \, (1-x_t)\).
  • To find the next value in the sequence, you substitute the most recent value you have calculated back into the equation to give you the next value, continuing this process until \(t=20\).
This repetitive nature of calculations helps us see how each value depends heavily on its predecessor. It gives a sequence of numbers that describe how the system evolves over each period, showing whether it stabilizes, oscillates, or diverges.
As you practice, the calculations become straightforward. This iterative process is a powerful way to observe changes and patterns over time in many mathematical and real-world systems.
Growth Rate Parameter
The growth rate parameter, denoted here as \(R_0\), plays a crucial role in the discrete logistic equation by controlling how strongly the value of \(x_t\) changes from one step to the next.
  • In our equation, \(R_0 = 3.1\), which is a constant value throughout the sequence calculations.
  • This parameter influences whether the sequence of \(x_t\) values increases, decreases, or stays relatively stable.
  • Higher growth rate values typically mean more rapid changes in the values of \(x_t\).
Understanding this parameter is essential because it dictates the dynamic behavior:
  • If \(R_0\) is too low, the population might die out.
  • If it’s too high, the population could oscillate chaotically.
By experimenting with different growth rate parameters, one can explore various behaviors such as stability, periodicity, or chaos in complex systems. This exploration can offer insights into population dynamics, economics, and various fields where growth processes are modeled.
Graphing Sequences
Graphing the sequence \(x_t\) versus time \(t\) offers a visual insight into the behavior and trends of the sequence created by the discrete logistic equation.
  • Here, \(t\) runs along the x-axis, representing the time steps from 0 to 20.
  • \(x_t\), running along the y-axis, showcases the value at each respective time step.
Creating a graph allows you to visually observe patterns, trends, and anomalies, making it an invaluable tool for analysis.
Some common observations include:
  • Whether the values stabilize, showing a steady line, or oscillate, indicating fluctuations.
  • Potential chaotic patterns that could imply a sensitive dependence on initial conditions.
  • Long-term behavior of the sequence, whether converging to a particular value or diverging.
For students, graphing transforms abstract numerical sequences into a more tangible form, providing a better understanding of how the sequence behaves over time. It is a crucial step as it visually reinforces the outcomes obtained through iterative calculations. By plotting graphs, you'll gain enhanced insights into the nature of the sequence and how such dynamic systems evolve. It’s an effective way to communicate the results of mathematical modeling and analysis.

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Most popular questions from this chapter

The sequence \(\left\\{a_{n} \mid\right.\) is recursively defined. Find all fixed points of \(\left[a_{n}\right\\} .\) $$ a_{n+1}=\frac{1}{3} a_{n}+\frac{4}{3} $$

Use the limit laws to determine \(\lim _{n \rightarrow \infty} a_{n}=a .\) $$ \lim _{n \rightarrow \infty} \frac{n+2^{-n}}{n} $$

Because of complex interactions with other drugs, some drugs have zeroth order elimination kinetics in some circumstances, and first order kinetics in other circumstances, depending on what other drugs are in the patient's system, as well as on age and preexisting medical conditions. Use the data on how concentration varies with time to determine whether the drug has zeroth or first order kinetics. Given the following sequence of measurements of drug concentration, determine whether the drug has zeroth or first order kinetics. $$ \begin{array}{lcccc} \hline \boldsymbol{t} \text { (Hours) } & 1 & 2 & 3 & 4 \\ \hline c_{t}(\mu \mathrm{g} / \mathrm{m} \mathrm{l}) & 20 & 18 & 16 & 14 \\ \hline \end{array} $$

Assume that the population growth is described by the Beverton-Holt recruitment curve with parameters \(R_{0}\) and a. Find the population sizes for \(t=1,2, \ldots, 5\) and find \(\lim _{t \rightarrow \infty} N_{t}\) for the given initial value \(N_{0} .\) \(R_{0}=2, a=0.1, N_{0}=2\)

Tylenol in the Body A patient is taking Tylenol (a painkiller that contains acetaminophen) to treat a fever. The data in this question is taken from Rawlins, Henderson, and Hijab (1977). At \(t=0\) the patient takes their first pill. One hour later the drug has been completely absorbed and the blood concentration, measured in \(\mu \mathrm{g} / \mathrm{ml}\), is 15 . Acetaminophen has first order elimination kinetics; in one hour, \(23 \%\) of the acetaminophen present in the blood is eliminated. (a) Write a recursion relation for the concentration \(c_{t}\) of drug in the patient's blood. For \(t \geq 1\) you may assume for now that no other pills are taken after the first one. (b) Find an explicit formula for \(c_{t}\) as a function of \(t\). (c) Suppose that the patient follows the directions on the pill box and takes another Tylenol pill 4 hours after the first (at time \(t=4\) ). What is the concentration at the time at which the second pill is taken? In others words, what is \(c_{4}\) ? (d) Over the next hour \(15 \mathrm{\mug} / \mathrm{ml}\) of drug enter the patient's bloodstream. So, \(c_{5}\) can be calculated from \(c_{4}\) using the word equation: $$ c_{5}=c_{4}+ $$ nt added \(\quad\) amount eliminated blo Given that the amount added is \(15 \mu \mathrm{g} / \mathrm{ml}\), and the amount eliminated is \(0.23 \cdot c_{4}\), calculate \(c_{5} .\) (e) For \(t=5,6,7,8\) the drug continues to be eliminated at a rate of \(23 \%\) per hour. No pills are taken and no extra drug enters the patient's blood. Compute \(c_{8}\). (f) At time \(t=8\), the patient takes another pill. Calculate \(c_{9} .\) Do not forget to include elimination of drug between \(t=8\) and \(t=9\). (g) We want to calculate the maximum concentration of drug in the patient's blood. We know that concentrations are highest in the hour after a pill is taken, namely at time \(t=1, t=5, t=\) \(9, \ldots\) Define a sequence \(C_{n}\) representing the concentration of the drug one hour after the \(n\) th pill is taken. (h) What terms of the original sequence \(\left\\{c_{r}: t=1,2, \ldots\right\\}\) are \(C_{1}\), \(C_{2}\), and \(C_{3} ?\) (i) Explain why $$ C_{n+1}=(0.77)^{4} \cdot C_{n}+15 $$ and \(c_{1}=15\) (j) From the recursion relation, assuming that the patient continues to take Tylenol pills at 4 -hour intervals, calculate \(C_{1}, C_{2}\), \(C_{3}, C_{4}, C_{5}\), and \(C_{6}\) (k) Does \(C_{n}\) increase indefinitely, or do you think that it converges? (1) By looking for fixing point of the recursion relation in (h), find the limit of \(C_{n}\) as \(n \rightarrow \infty\).

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