to 2000. Similarly negative correlation can be found for the double-peaked broad H$\alpha$ of NGC1097 (Schimoia et al. 2012, Storchi-Bergmann et al. 2003). However, through study of one sample of double-peaked emitters, Lewis et al. (2010) have shown that there is no confirmed correlation between the peak separation and the line flux for long-term observed double-peaked broad H$\alpha$, and additionally, the expected negative correlation between the line width (either FWHM or FWQM) and the broad H$\alpha$ flux is not observed. The contradictory is mainly due to the following reason: there are important effects on peak separation from varying of physical disk parameters, such as the effects from accretion disk precession, in the context of the accretion disk model for double-peaked emitters.

As we have seen that the proposed accretion disk models for double-peaked emitters lead to one important result: disk precession (or physical disk structure parameters varying) dominates the line profile variations of double-peaked broad line, besides the not so important contributions from the other subtle structures, such as the hot spots, warped structures etc.. In some cases, such as disk-like BLR with large eccentricity $e\sim0.4$ under the elliptical accretion disk model, even there were no variations of continuum emission, 