Math Problem Statement

Consider the following logistic discrete-time dynamical system.

xt+1  = 9 10 xt(1 − xt)

(a) Consider the following statements.

(i) The per capita production of this system is a constant function. (ii) The derivative of the updating function is an increasing function.

Determine which of the above statements are True (1) or False (2).

So, for example, if you think that the answers, in the above order, are True,False, then you would enter '1,2' into the answer box below (without the quotes).

(b) Determine the non-zero equilibrium of this system. (c) Which statement best describes the stability of the equilibria for this system?

(A) The non-zero equilibrium is stable; 0 is an unstable equilibrium. (B) The non-zero equilibrium is unstable; 0 is an unstable equilibrium. (C) The non-zero equilibrium is half-stable; 0 is a stable equilibrium. (D) The non-zero equilibrium is stable; 0 is a half-stable equilibrium. (E) The non-zero equilibrium is stable; 0 is a stable equilibrium. (F) The non-zero equilibrium is half-stable; 0 is an unstable equilibrium. (G) The non-zero equilibrium is unstable; 0 is a half-stable equilibrium. (H) The non-zero equilibrium is unstable; 0 is a stable equilibrium.

Solution

Problem Analysis:

We analyze each part of the problem systematically to determine the answers.


(a) Evaluating the Statements:

The logistic discrete-time dynamical system is: xt+1=910xt(1xt),x_{t+1} = \frac{9}{10} x_t (1 - x_t), where the updating function is f(x)=910x(1x)f(x) = \frac{9}{10} x (1 - x).

  1. Per capita production: Per capita production is defined as f(x)x=910(1x)\frac{f(x)}{x} = \frac{9}{10}(1 - x) (for x0x \neq 0). This is a linear function of xx, not a constant function. Thus, statement (i) is False.

  2. Derivative of the updating function: Compute f(x)f'(x): f(x)=ddx(910x(1x))=910(12x).f'(x) = \frac{d}{dx} \left( \frac{9}{10} x (1 - x) \right) = \frac{9}{10} (1 - 2x). The derivative is a decreasing linear function because 12x1 - 2x decreases as xx increases. Thus, statement (ii) is False.

Answer for Part (a):

2,2


(b) Non-Zero Equilibrium:

To find equilibria, solve xt+1=xtx_{t+1} = x_t, i.e., f(x)=xf(x) = x: 910x(1x)=x.\frac{9}{10} x (1 - x) = x. Factorizing: 910x910x2=x    910xx910x2=0    x(110910x)=0.\frac{9}{10} x - \frac{9}{10} x^2 = x \implies \frac{9}{10} x - x - \frac{9}{10} x^2 = 0 \implies x \left( -\frac{1}{10} - \frac{9}{10} x \right) = 0. The solutions are: x=0andx=19/10=109.x = 0 \quad \text{and} \quad x = -\frac{1}{9/10} = \frac{10}{9}. Since xx represents a fraction of a population (non-negative), only x=109x = \frac{10}{9} is relevant.

Answer for Part (b):

Non-zero equilibrium: x=109x = \frac{10}{9}.


(c) Stability of Equilibria:

To determine the stability, compute f(x)|f'(x)| at each equilibrium point.

  1. At x=0x = 0: f(x)=910(12x)    f(0)=910.f'(x) = \frac{9}{10} (1 - 2x) \implies f'(0) = \frac{9}{10}. Since f(0)<1|f'(0)| < 1, x=0x = 0 is a stable equilibrium.

  2. At x=109x = \frac{10}{9}: f(x)=910(12x)    f(109)=910(12109)=910(1209)=910(119)=9990.f'(x) = \frac{9}{10} (1 - 2x) \implies f'\left(\frac{10}{9}\right) = \frac{9}{10} \left(1 - 2 \cdot \frac{10}{9}\right) = \frac{9}{10} \left(1 - \frac{20}{9}\right) = \frac{9}{10} \cdot \left(-\frac{11}{9}\right) = -\frac{99}{90}. Since f(109)=9990>1|f'(\frac{10}{9})| = \frac{99}{90} > 1, x=109x = \frac{10}{9} is an unstable equilibrium.

Answer for Part (c):

(H) The non-zero equilibrium is unstable; 0 is a stable equilibrium.


Final Answers:

  1. (a): 2,22,2
  2. (b): x=109x = \frac{10}{9}
  3. (c): H: The non-zero equilibrium is unstable; 0 is a stable equilibrium.\text{H: The non-zero equilibrium is unstable; 0 is a stable equilibrium.}

Would you like further explanation on any part of the analysis or derivation?


Related Questions:

  1. How does the derivative of a logistic function affect equilibrium stability?
  2. What happens to the population xtx_t if x0>109x_0 > \frac{10}{9}?
  3. What is the biological interpretation of stability in this model?
  4. Can a logistic map with a different growth factor (rr) have multiple stable equilibria?
  5. How is the concept of per capita growth applied in real-world models?

Tip:

When analyzing stability, always compute f(x)|f'(x)| at the equilibrium points to determine whether they are stable (f(x)<1|f'(x)| < 1) or unstable (f(x)>1|f'(x)| > 1).

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Math Problem Analysis

Mathematical Concepts

Logistic Map
Discrete-Time Dynamical Systems
Equilibrium Points
Stability Analysis

Formulas

x_{t+1} = (9/10) x_t (1 - x_t)
f'(x) = (9/10)(1 - 2x)
f(x) = (9/10) x (1 - x)

Theorems

Equilibrium Point Analysis
Stability of Fixed Points
Derivative and Stability Criteria

Suitable Grade Level

Grades 11-12