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・ Fermat's Last Theorem (book)
・ Fermat's Last Theorem in fiction
・ Fermat's little theorem
・ Fermat's principle
・ Fermat's right triangle theorem
・ Fermat's Room
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・ Fermat's theorem
・ Fermat's theorem (stationary points)
・ Fermat's theorem on sums of two squares
・ Fermata
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・ Fermat–Catalan conjecture
・ Fermat–Weber problem
Fermat’s and energy variation principles in field theory
・ Fermax
・ Ferme castrale of Hermalle-sous-Huy
・ Ferme de la Rançonnière
・ Ferme des Greves Aerodrome
・ Ferme générale
・ Ferme ornée
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・ Ferment (album)
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・ Fermentation (disambiguation)
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Fermat’s and energy variation principles in field theory : ウィキペディア英語版
Fermat’s and energy variation principles in field theory
In general relativity the light is assumed to propagate in the vacuum along null geodesic in a pseudo-Riemannian manifold. Besides the geodesics principle in a classical field theory there exists the Fermat's principle for stationary gravity fields. Belayev has proposed variational method without the violation of isotropy of the path of the lightlike particle, giving equations identical to those that follow from Fermat's principle. In this method the action principle leads to condition of zero variational derivative of the integral of energy, and it is applied also to non-stationary gravity fields.
== Fermat's principle ==

In more general case for conformally stationary spacetime with coordinates (t,x^1,x^2,x^3) a Fermat metric takes form
g=e^(dx^ dx^ ),
where conformal factor f(t,x) depending on time t and space coordinates x^ does not affect the lightlike geodesics apart from their parametrization.
Fermat's principle for a pseudo-Riemannian manifold states that the light ray path between points x_a=(x^1_a,x^2_a,x^3_a) and x_b=(x^1_b,x^2_b,x^3_b) corresponds to zero variation of action
S=\int^_\left(\sqrt \frac \frac}+\phi_(x)\frac \right)d\mu,
where \mu is any parameter ranging over an interval (\mu_b ) and varying along curve with fixed endpoints x_a=x(\mu_a) and x_b=x(\mu_b).

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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