One of the main drawbacks of the integral equations method applied to
scattering problems is that, after discretization, this method leads t
o a full complex and non-Hermitian matrix. Furthermore, as the mathema
tical problem may be singular due to eigenvalues of the inside problem
of diffraction, the matrix is usually ill-conditioned. In this paper,
we study a preconditioning matrix from the point of view of efficienc
y and parallelism.