Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Aligned electric and magnetic Weyl fields   We analyze the spacetimes admitting a direction for which the relative
electric and magnetic Weyl fields are aligned. We give an invariant
characterization of these metrics and study the properties of its Debever null
vectors. The directions 'observing' aligned electric and magnetic Weyl fields
are obtained for every Petrov type. The results on the no existence of purely
magnetic solutions are extended to the wider class having homothetic electric
and magnetic Weyl fields.

4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
3
The categories of this paper are: physics
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph