Quadratic Forms and Closed Geodesics
Quadratic Forms and Closed Geodesics
Quadratic Forms and Closed Geodesics
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Pell’s Equation<br />
<strong>Quadratic</strong> <strong>Forms</strong><br />
<strong>and</strong> <strong>Closed</strong><br />
<strong>Geodesics</strong><br />
Y. Petridis<br />
◮ Algorithm for solving<br />
x 2 − 2y 2 = ±1<br />
(Pythagoreans)<br />
◮ Start with<br />
◮ We get<br />
x 1 = 1, y 1 = 1<br />
(x 2 , y 2 ) = (3, 2)<br />
(x 3 , y 3 ) = (7, 5)<br />
(x 4 , y 4 ) = (17, 12)<br />
◮ Recurrences<br />
x n+1 = x n + 2y n<br />
y n+1 = x n + y n<br />
◮ Fundamental solution:<br />
1 + √ 2<br />
x n + √ 2y n = (1 + √ 2) n<br />
<strong>Quadratic</strong> <strong>Forms</strong><br />
Hyperbolic<br />
surfaces<br />
<strong>Closed</strong><br />
<strong>Geodesics</strong><br />
Spectral Theory