# U_g2l_state

The page document the user-supplied call-back routine `U_g2l_state`

.

The routine `U_g2l_state`

is a call-back routine that has to be provided by the user. In the simplified interface the predefined name of the routine is `g2l_state_pdaf`

, but in the full interface, the user can choose the name of the routine.
The routine is used with all filter algorithms using domain-localization (LSEIK, LETKF, LESTKF) and is independent of the particular algorithm.
The routine is called during the loop over the local analysis domains in the analysis step. It has to provide the local state vector that corresponds to the specified local analysis domain. Provided to the routine is the state vector `state_p`

. With a domain decomposed model, this is the state for the process-local model sub-domain.

The interface is the following:

SUBROUTINE U_g2l_state(step, domain_p, dim_p, state_p, dim_l, state_l)

with

`step`

:`integer, intent(in)`

Current time step`domain_p`

:`integer, intent(in)`

Index of current local analysis domain`dim_p`

:`integer, intent(in)`

Dimension of state vector for parallel model sub-domain`dim_l`

:`integer, intent(in)`

Dimension of state vector in local analysis domain`state_p`

:`integer, intent(in), dimension(dim_p)`

State vector for parallel model sub-domain`state_l`

:`integer, intent(out), dimension(dim_l)`

State vector on local analysis domain

Hints:

- In the simple case that a local analysis domain is a single point of the model grid, the operation in this routine would be to take out of
`state_p`

the data (i.e. the different model fields) for the grid point corresponding to the index`domain_p`

.