Inclusion of an automatic adaptive sampling method in NEC

As sampling is taking place, the most active regions of the spectrum can be identified (i.e. the vicinity of spectral peaks). By selectively increasing the spectral density within those regions improves the quality of the total spectral representation reducing at the same time the global number of samples, and therefore, the total calculation time. The Blumer index is useful for adapting the sampling density of a calculated or measured spectrum.