Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Periodic Solutions of Non-Autonomous Second Order Hamiltonian Systems   We try to generalize a result of M. Willem on forced periodic oscillations
which required the assumption that the forced potential is periodic on spatial
variables. In this paper, we only assume its integral on the time variable is
periodic, and so we extend the result to cover the forced pendulum equation. We
apply the direct variational minimizing method and Rabinowtz's saddle point
theorem to study the periodic solution when the integral of the potential on
the time variable is periodic.

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The categories of this paper are: plasm-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: adap-org
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The categories of this paper are: hep-ex
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The categories of this paper are: nlin
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The categories of this paper are: supr-con
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-ex
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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio
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The categories of this paper are: ao-sci
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The categories of this paper are: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: dg-ga