# Difference between revisions of "CDS 140a Winter 2013 Homework 4"

Jump to: navigation, search

 WARNING: This homework set is still being written. Do not start working on these problems until this banner is removed.

 R. Murray, D. MacMartin Issued: 29 Jan 2013 (Tue) ACM 101/AM 125b/CDS 140a, Winter 2013 Due: 5 Feb 2013 (Tue)
__MATHJAX__

Note: In the upper left hand corner of the second page of your homework set, please put the number of hours that you spent on this homework set (including reading).

(Not yet edited from 2011)

1. Perko, Section 2.7, problem 1 Write the system
<amsmath>

\dot{x}_1=x_1+6x_2+x_1x_2,\qquad \dot{x}_2=4x_1+3x_2-x_1^2

</amsmath>

in the form

<amsmath>

\dot{y}=By+G(y)

</amsmath>

where

<amsmath>

B=\begin{bmatrix}\lambda_1&0\\0&\lambda_2\end{bmatrix}

</amsmath>

with $\lambda_1<0$, $\lambda_2>0$ and $G(y)$ is quadratic in $y_1$ and $y_2$.

2. Perko, Section 2.7, problem 2 Find the first three successive approximations $u^{(1)}(t,a)$, $u^{(2)}(t,a)$, and $u^{(3)}(t,a)$ for
<amsmath>

\dot{x}_1=-x_1,\qquad \dot{x}_2=x_2+x_1^2

</amsmath>

and use $u^{(3)}(t,a)$ to approximate $S$ near the origin. Also approximate the unstable manifold $U$ near the origin for this system. Note that $u^{(2)}(t,a)=u^{(3)}(t,a)$ and therefore $u^{(j+1)}(t,a)=u^{(j)}(t,a)$ for $j\geq 2$. Thus $u(t,a)=u^{(2)}(t,a)$ which gives the exact function defining $S$.

3. Perko, Section 2.7, problem 3 Solve the system in Problem 2 and show that $S$ and $U$ are given by
<amsmath>

S:\,x_2=-\frac{x_1^2}{3}

</amsmath>
<amsmath>

U:\,x_1=0

</amsmath>

Sketch $S$, $U$, $E^s$ and $E^u$.

4. Repeat problem 2 and 3 above using Taylor series for $h(x)$ to define $S=\{(x_1,x_2)|x_2=h(x)\}$ and matching coefficients to solve for $h(x)$.
5. Perko, Section 2.9, problem 2(a)(b) Determine the stability of the equilibrium points of the system (1) with $f(x)$ given by
<amsmath>

(a)\quad\begin{bmatrix}x_1^2-x_2^2-1\\2x_2\end{bmatrix}

</amsmath>
<amsmath>

(b)\quad\begin{bmatrix}x_2-x_1^2+2\\2x_2^2-2x_1x_2\end{bmatrix}

</amsmath>

Notes:

• The problems are transcribed above in case you don't have access to Perko. However, in the case of discrepancy, you should use Perko as the definitive source of the problem statement.

1. Perko, Section 2.7, problem 1
2. Perko, Section 2.7, problem 2
3. Perko, Section 2.7, problem 3
4, 5. Choose any 2 of the following:
• Perko, Section 2.7, problem 4
• Perko, Section 2.7, problem 5
• Perko, Section 2.7, problem 6
• Perko, Section 2.8, problem 1
6. Perko, Section 2.9, problem 2(a)(b)