# U_init_obsvar_l

The page documents the user-supplied call-back routine `U_init_obsvar_l`

.

The routine `U_init_obsvar_l`

is a call-back routine that has to be provided by the user. In the simplified interface the predefined name of the routine is `init_obsvar_l_pdaf`

, but in the full interface, the user can choose the name of the routine.
The routine is called in the local filters during the loop over all local analysis domains by the routine that computes a local adaptive forgetting factor (`PDAF_set_forget_l`

). The routine has to initialize a local mean observation error variance for all observations used for the analysis in the specified local analysis domain.
The routine is only called if the local adaptive forgetting factor is used (`type_forget=2`

in the example implementation). When the routine is called it has to return the mean observation error variance for the local observation domain.

The interface is the following:

SUBROUTINE U_init_obsvar_l(domain_p, step, dim_obs_l, obs_l, meanvar_l)

with

`domain_p`

:`integer, intent(in)`

Index of current local analysis domain`step`

:`integer, intent(in)`

Current time step`dim_obs_l`

:`integer, intent(in)`

Local dimension of observation vector`obs_l`

:`real, intent(in), dimension(dim_obs_p)`

Local observation vector`meanvar_l`

:`real, intent(out)`

Mean local observation error variance

Notes:

- If the local adaptive forgetting factor is not used, this routine has only to exist for the compilation, but it does not need functionality.