Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the generalization of wavelet diagonal preconditioning to the
  Helmholtz equation   We present a preconditioning method for the multi-dimensional Helmholtz
equation with smoothly varying coefficient. The method is based on a frame of
functions, that approximately separates components associated with different
singular values of the operator. For the small singular values, corresponding
to propagating waves, the frame functions are constructed using ray theory. A
series of 2-D numerical experiments demonstrates that the number of iterations
required for convergence is small and independent of the frequency. In this
sense the method is optimal.

26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
4
The categories of this paper are: cond-mat