Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Sparse Eigenvectors of the Discrete Fourier Transform   We construct a basis of sparse eigenvectors for the N-dimensional discrete
Fourier transform. The sparsity differs from the optimal by at most a factor of
four. When N is a perfect square, the basis is orthogonal.

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The categories of this paper are: physics
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: eess
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The categories of this paper are: acc-phys
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ex
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The categories of this paper are: astro-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: econ
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The categories of this paper are: q-alg