Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effects of the core radius of an isothermal ellipsoidal gravitational
  lens on the caustics and the critical curves   We study the effect of the core radius of an isothermal ellipsoidal
gravitational lens on the caustics and the critical curves. We derive an
analytic expression of the caustics for an isothermal ellipsoidal gravitational
lens via a sixth-order algebraic equation. Since the expression is too long, by
using another method we obtain a parametric representation of the critical
curves in order to show analytically that there exist three cases: There are
two curves for a small core radius, one for a quite large one, and no curves
appear for an extremely large one, though the latter two cases are not
realistic. The caustics are represented also by the same parameter.

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The categories of this paper are: bayes-an
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The categories of this paper are: q-bio
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The categories of this paper are: stat
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
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The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph