Description

Homework guidelines for writers:

(Adapted from the website of Professor Andy Ruina). To get full credit, please do these things on each homework.
MA 508
HW 3
On the top right corner, please put your group number, the names of your group members, with the writer at the top and clearly indicated. Also indicate any non-participating group members, e.g.:
Group 3
Jaromir Jagr (writer)
Sarah Jessica Parker
Michelle Wie
James Van der Beek (did not participate)
4. Your work should be laid out neatly enough to be read by someone who does not know how to do theproblem. For most jobs, it is not sufficient to know how to do a problem, you must convince others that you know how to do it. Your job on the homework is to practice this. Box your answers.
This homework covers 1. Transcritical bifurcations; 2. Pitchfork bifurcations (super- and subcritical); 3. Hysteresis; and 4. Imperfect bifurcations.
These topic are covered in §3.2-3.6 in Strogatz.

For your bifurcation diagrams:
i. Indicate stable fixed points with a solid line and unstable fixed points with a dashed line ii. Show your calculations for how you determined the fixed points iii. Explain how you determined stability and/or show your calculations iv. Clearly indicate any bifurcation(s) (if they exist)
v. Clearly identify and label bifurcation(s) (saddle-node, transcritical, pitchfork, if they exist)

1. Consider the equation
x˙ = ax−x(1 −x)2 (1)
a) Draw a bifurcation diagram for this equation as a varies.
b) In the neighborhood of all bifurcation(s), if they exist, transform Eq. 1 into the normal form.

2. Consider the following bifurcation diagram, showing fixed points (x∗) as a function of parameter, p, for an equation of the form ˙x = f(x). Note that there are three different parameter values indicated, p1, p2, and p3.

Figure 1: Bifurcation diagram; stable fixed points are drawn as a solid line, unstable as a dashed line.
a) Label and identify all bifurcations in the figure.
b) Draw phase portraits consistent with the bifurcation curve at each of the parameter values, p1, p2 and p3. (You should draw one plot for each parameter value, a total of three phase portraits). c) Can this system exhibit hysteresis (according to the definition used in class)?
d) How would your answer to c) change if the stability in Fig. 1 were flipped (i.e., each stable fixed point were unstable, and each unstable fixed point were stable)? Explain.

3. Here is the equation for an imperfect transcritical bifurcation
b) Sketch a stability diagram (Recall that a stability diagram will have a and ε as axes, and will indicated regions where there are differing numbers of fixed points).