# CDS 140b Spring 2014 Homework 2

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 R. Murray, D. MacMartin Issued: 9 Feb 2014 (Wed) CDS 140b, Spring 2014 Due: 16 Feb 2014 (Wed)
__MATHJAX__

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UNDER CONSTRUCTION, DO NOT START

1. Perko, Section 3.3, problem 5. Show that
<amsmath>\aligned

\dot x &=y+y(x^2+y^2)\\ \dot y &=x-x(x^2+y^2)

\endaligned</amsmath>

is a Hamiltonian system with $4H(x,y)=(x^2+y^2)^2-2(x^2-y^2)$. Show that $dH/dt=0$ along solution curves of this system and therefore that solution curves of this system are given by

<amsmath>

(x^2+y^2)^2-2(x^2-y^2)=C

</amsmath>

Show that the origin is a saddle for this system and that $(\pm 1,0)$ are centers for this system. (Note the symmetry with respect to the $x$-axis.) Sketch the two homoclinic orbits corresponding to $C=0$ and sketch the phase portrait for this system. (You need not comment on the compound separatrix cycle.)