# ARTS built-in documentation server

## Workspace Method abs_linesPopulation

### Description

Sets population type for all lines.
Available ``option``:
- ``"LTE"``: Assume band is in LTE
- ``"NLTE"``: Assume band is in NLTE and the upper-to-lower ratio is known
- ``"VibTemps"``: Assume band is in NLTE described by vibrational temperatures and LTE at other levels
- ``"ByHITRANRosenkranzRelmat"``: Assume band needs to compute relaxation matrix to derive HITRAN Y-coefficients
- ``"ByHITRANFullRelmat"``: Assume band needs to compute and directly use the relaxation matrix according to HITRAN
- ``"ByMakarovFullRelmat"``: Assume band needs to compute and directly use the relaxation matrix according to Makarov et al 2020
- ``"ByRovibLinearDipoleLineMixing"``: Assume band needs to compute and directly use the relaxation matrix according to Hartmann, Boulet, Robert, 2008, 1st edition
You must have set nlte_field and/or its ilk to use the NLTE methods.
You must have abs_hitran_relmat_data for the ByHITRANXX methods.
You must have ecs_data for the other two relaxation matrix options

**Authors: **Richard Larsson

### Synopsis

### Variables