Science:Math Exam Resources/Courses/MATH103/April 2013/Question 05 (a)

MATH103 April 2013

  •  Q1 (a)  •  Q1 (b)  •  Q1 (c)  •  Q1 (d)  •  Q1 (e)  •  Q1 (f)  •  Q2 (a)  •  Q2 (b)  •  Q2 (c)  •  Q2 (d)  •  Q3 (a)  •  Q3 (b) i  •  Q3 (b) ii  •  Q4 (a)  •  Q4 (b)  •  Q5 (a)  •  Q5 (b)  •  Q6 (a)  •  Q6 (b)  •  Q6 (c)  •  Q7 (a)  •  Q7 (b)  •  Q7 (c)  •  Q7 (d)  •  Q7 (e)  •  Q8 (a)  •  Q8 (b)  •  Q8 (c)  •  Q9  •  Q10  •  

   Other MATH103 Exams

  •  April 2006  •  April 2005  •  April 2011  •  April 2010  •  April 2009  •  April 2012  •  April 2013  •  April 2014  •  April 2015  •  April 2016  •  April 2017  •  

Question 05 (a)
Consider the iterated map $\displaystyle x_{t+1}=4x_{t}^{3}-12x_{t}^{2}+8x_{t}$. Calculate the steady states (fixed-points, equilibria) and mark them in the sketch below. Determine the stability of each equilibrium (explain analytically or graphically). Plot a cobweb starting with $\displaystyle x_{0}$ just above 2 (the point is indicated in the sketch).

Make sure you understand the problem fully: What is the question asking you to do? Are there specific conditions or constraints that you should take note of? How will you know if your answer is correct from your work only? Can you rephrase the question in your own words in a way that makes sense to you?

If you are stuck, check the hint below. Consider it for a while. Does it give you a new idea on how to approach the problem? If so, try it!

Hint
Recall in this setting, steady states are found by setting $\displaystyle x_{t+1}=x_{t}$.

Checking a solution serves two purposes: helping you if, after having used the hint, you still are stuck on the problem; or if you have solved the problem and would like to check your work. If you are stuck on a problem: Read the solution slowly and as soon as you feel you could finish the problem on your own, hide it and work on the problem. Come back later to the solution if you are stuck or if you want to check your work. If you want to check your work: Don't only focus on the answer, problems are mostly marked for the work you do, make sure you understand all the steps that were required to complete the problem and see if you made mistakes or forgot some aspects. Your goal is to check that your mental process was correct, not only the result.

Solution

Found a typo? Is this solution unclear? Let us know here. Please rate my easiness! It's quick and helps everyone guide their studies. The steady states are given by solving $\displaystyle x=4x^{3}-12x^{2}+8x$ Subtracting x from both sides yields $\displaystyle 0=4x^{3}-12x^{2}+7x=x(4x^{2}-12x+7)$ Using the quadratic formula gives $x={\frac {12\pm {\sqrt {144-4(4)(7)}}}{8}}={\frac {12\pm {\sqrt {32}}}{8}}={\frac {3\pm {\sqrt {2}}}{2}}$ Analytically to check stability, we would need to take the derivative of our function and then plug in the fixed points and check that the absolute value of the derivatives in the fixed points is less than 1 (this would show that the fixed point is stable). It's easier to notice that graphically, none of the fixed points are the limit of an iterative sequence and so none of the fixed points are stable.

Click here for similar questions

MER QGH flag, MER QGQ flag, MER QGS flag, MER QGT flag, MER Tag Sequences, Pages using DynamicPageList3 parser function, Pages using DynamicPageList3 parser tag