Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How distant is the ideal filter of being a causal one?   In this paper the characterization as convolution operators of filters
sending finite energy signals to bounded signals is used to prove several
theoretical results concerning the distance between the ideal filter and the
spaces of physically realizable filters. Both the analog and the digital cases
are studied and the formulas for the distance and the angle between the filters
in each case are also given.

33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga