bw - Adaptive broadening tool for NRG Ljubljana
Rok Zitko, rok.zitko@ijs.si, 2009

The algorithm used is described in the following paper:
A. Freyn, S. Florens, PRB 79, 121102(R) (2009).

NOTES: 

1. For very sharp features in the spectral function, there is a compromise
between the lowest b(w) allowed, 'bmin', and the fineness of the
discretization mesh, as controlled by 'broaden_ratio':

broaden_ratio - 1 << bmin.

In practice, bmin = broaden_ratio-1 is an adequate choice (order 10^-4 error).
