= PDAF_local_weights = 

This page documents the routine `PDAF_local_weights` of PDAF. 

The routine is used for localization in the analysis step of a filter and computes weights according to the specified distances and the settings for the localizing function. The routine can be called in [wiki:prodRinvA_l_pdaf prodRinvA_l_pdaf] in the domain-localized filters. Also, the routine can be used for the LEnKF in the routine [localize_covar_pdaf localize_covar_pdaf].

This routine is usually only used in user-codes that do not use PDAF-OMI. 

The interface is the following:
{{{
  SUBROUTINE PDAF_local_weights(wtype, cradius, sradius, distance, &
     weights, verbose)
}}}
with the following arguments:
 * `wtype` : `integer, intent(in)`[[BR]] Type of weight function:[[BR]] (0) unit weight (=1 up to radius `cradius`) [[BR]] (1) exponential decrease (1/e at distance=sradius; 0 for distance>cradius)[[BR]] (2) 5th order polynomial with support radius sradius (Gaspari&Cohn 1999; 0 for distance>sradius)
 * `cradius` : `real, intent(in)`[[BR]] Cut-off radius (weight is always =0 for distance>cradius)
 * `sradius` : `real, intent(in)`[[BR]] Support radius of weight function
 * `dim` : `integer, intent(in)`[[BR]] Size of arrays `distance` and `weights'
 * `distance` : `real, intent(in)`[[BR]] Distance to observation
 * `weights` : `real, intent(out)`[[BR]] computed localization weight
 * `verbose` : `integer, intent(in)`[[BR]] Verbosity flag

Notes:
 * `PDAF_local_weights` does not support the regulated localization method (Nerger et al. ,Quarterly Journal of the Royal Meteorological Society, 138 (2012) 802-812; see [wiki:PublicationsandPresentations Publications]). To use the regulated localization one has to use the alternative routine [wiki:PDAF_local_weight PDAF_local_weight].

There are currently only examples of using `PDAF_local_weight`, but not `PDAF_local_weights`. The examples for using `PDAF_local_weight` can be found in the files `prodrinva_l_pdaf.F90` in the tutorial cases for the 'classical' (non-OMI) implentations in `tutorial/classical` and in the templates in templates/classical/.