Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: $\mathcal{H}$-matrix approximability of inverses of FEM matrices for the
  time-harmonic Maxwell equations   The inverse of the stiffness matrix of the time-harmonic Maxwell equation
with perfectly conducting boundary conditions is approximated in the blockwise
low-rank format of ${\mathcal H}$-matrices. We prove that root exponential
convergence in the block rank can be achieved if the block structure conforms
to a standard admissibility criterion.

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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
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The categories of this paper are: acc-phys