detrend_local_()
This function detrends rho-delta plot (see the bottom figure) in order to identify cluster centers that have high delta values (distance to nearest neighbor having higher density rho). The detrend is done by fitting a quadratic function in delta vs. log(rho) plot.
If P.vcDetrend_postclu = 'global', single fitting is done to all sites.
If P.vcDetrend_postclu = 'local', separate fitting is done to each site.
Once the detrending is done, outliers (cluster peaks) are identified by searching for events exceeding P.delta1_cut (distance) and P.rho_cut (density) thresholds.