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Investigate the effect of the parameter \(C\) on the logistic curve $$P=\frac{10}{1+C e^{-t}}$$ Substitute several values for \(C\) and explain, with a graph and with words, the effect of \(C\) on the graph.

Short Answer

Expert verified
The parameter \( C \) controls the initial growth rate and level: smaller \( C \) means faster and higher starting growth, while larger \( C \) slows the growth.

Step by step solution

01

Understanding the Logistic Function

The logistic function given is \( P = \frac{10}{1 + C e^{-t}} \). This function models growth where \( P \) approaches a maximum of 10 as \( t \) increases. The parameter \( C \) affects the rate and the initial value of growth.
02

Substitutions for Small Values of C

Substitute small values for \( C \), such as \( C = 0.1, 0.5, 1 \). For small \( C \), the curve starts higher, closer to the maximum value of 10, and rises quickly because \( C e^{-t} \) becomes very small, reducing the effect of the term in the denominator.
03

Substitutions for Larger Values of C

Now substitute larger values, such as \( C = 5, 10, 20 \). For large \( C \), the curve starts lower, as more of \( t \)'s effect through the exponential term \( e^{-t} \) slows down reaching the maximum hence growth starts slower.
04

Graphical Representation

Plot the function \( P(t) \) for several values like \( C = 0.1, 0.5, 1, 5, 10, 20 \). Observe that as \( C \) increases, the initial value of \( P \) decreases and the time it takes for \( P \) to approach 10 increases. Therefore, the larger \( C \) gets, the slower \( P \) rises towards its maximum.
05

Conclusion on the Effect of C

In conclusion, the parameter \( C \) affects the steepness and the starting point of the logistic curve. Lower values of \( C \) cause the function to start high and grow quickly, while higher values of \( C \) slow down the initial growth and flatten the curve.

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Key Concepts

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

Parameters Effect
In the study of logistic growth, understanding how parameters affect the model is crucial. The logistic function given by \( P = \frac{10}{1+C e^{-t}} \) provides insights into how different values of \( C \) influence the curve's shape. The parameter \( C \) plays a significant role in determining the behavior of the curve.

When you substitute small values for \( C \) such as 0.1 or 0.5, the curve starts relatively high. This is because the term \( C e^{-t} \) becomes quite small quickly, exerting little influence on the denominator. Consequently, the value of \( P \) approaches its maximum rapidly. As \( C \) gets larger, for instance 10 or 20, the initial value of \( P \) is lower. This occurs because \( C \) amplifies the effect of the exponential term \( e^{-t} \), making it take longer to reduce and allowing \( P \) to grow towards its maximum more gradually.
  • Small \( C \): The curve rises quickly, reaching the maximum value faster.
  • Large \( C \): Slower initial growth, resulting in a flattened curve that takes more time to reach the maximum.
The varying influence of \( C \) on the curve highlights its importance in shaping the logistic growth model.
Growth Models
Growth models help describe how populations grow over time subject to limitations. Logistic growth is a classic model used when population growth is slowed down by environmental factors. This contrasts with unrestricted exponential growth.

The logistic model represented by \( P = \frac{10}{1+C e^{-t}} \) illustrates how growth starts off nearly exponential but slows as it approaches a carrying capacity, in this case, 10. The carrying capacity is the maximum population size that the environment can sustain indefinitely. Logistic growth is important because it represents more realistic scenarios compared to exponential models. In many natural systems, resources become limited as the population grows, causing the growth rate to decrease as the population nears its carrying capacity.
  • Logistic Growth: Growth over time limited by carrying capacity.
  • Exponential Growth: Constant rate, unlimited resources.
This logistic growth model is practical for understanding population dynamics in ecology, epidemiology, and resource management.
Logistic Function
The logistic function is a powerful tool for modeling bounded growth. The function \( P = \frac{10}{1+C e^{-t}} \) specifically represents how an entity grows towards a maximum limit of 10 over time. Understanding how the logistic function operates provides clarity on various real-world growth scenarios.

The key components of the logistic function include:
  • Carrying Capacity: The maximum achievable value, here 10, which \( P \) cannot exceed.
  • Rate of Growth: Modulated by the parameter \( C \), influencing how rapidly or slowly the function approaches its carrying capacity.
As time \( t \) progresses, the exponential term \( e^{-t} \) diminishes, lessening its impact. At initial times, especially with a lower \( C \), the function rises quickly but as \( t \) increases, the growth rate slows and \( P \) levels off, asymptotically approaching 10.

This behavior makes the logistic function essential for modeling contexts like population growth, the spread of diseases, or any scenario where growth is naturally self-limiting. Its ability to model both rapid initial growth and eventual stabilization is why it's favored in various scientific and practical applications.

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Most popular questions from this chapter

In the spring of \(2003,\) SARS (Severe Acute Respiratory Syndrome) spread rapidly in several Asian countries and Canada. Table 4.9 gives the total number, \(P\), of SARS cases reported in Hong Kong \(^{17}\) by day \(t,\) where \(t=0\) is March 17,2003. (a) Find the average rate of change of \(P\) for each interval in Table 4.9 (b) In early April \(2003,\) there was fear that the disease would spread at an ever-increasing rate for a long time. What is the earliest date by which epidemiologists had evidence to indicate that the rate of new cases had begun to slow? (c) Explain why an exponential model for \(P\) is not appropriate. (d) It turns out that a logistic model fits the data well. Estimate the value of \(t\) at the inflection point. What limiting value of \(P\) does this point predict? (e) The best-fitting logistic function for this data turns out to be $$P=\frac{1760}{1+17.53 e^{-0.1408 t}}$$ What limiting value of \(P\) does this function predict? Total number of SARS cases in Hong Kong by day \(t\) (where \(t=0\) is March 17,2003) $$\begin{array}{c|c|c|c|c|c|c|c}t & P & t & P & t & P & t & P \\\\\hline 0 & 95 & 26 & 1108 & 54 & 1674 & 75 & 1739 \\\5 & 222 & 33 & 1358 & 61 & 1710 & 81 & 1750 \\\12 & 470 & 40 & 1527 & 68 & 1724 & 87 & 1755 \\\19 & 800 & 47 & 1621 & & & & \\\\\hline\end{array}$$

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