Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Matrix methods for wave equations   In analogy to a characterisation of operator matrices generating
$C_0$-semigroups due to R. Nagel (\cite{[Na89]}), we give conditions on its
entries in order that a $2\times 2$ operator matrix generates a cosine operator
function. We apply this to systems of wave equations, to second order
initial-boundary value problems, and to overdamped wave equations.

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The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
11
The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
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The categories of this paper are: nlin
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
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The categories of this paper are: eess