# ARTS built-in documentation server

## Workspace Method abs_lookupSetup

### Description

Set up input parameters for abs_lookupCalc. More information can be found in the documentation for method abs_lookupSetupBatch Max and min values of H2O and temperature are adjusted to allow for numerical perturbations in Jacobian calculation. The input variables abs_nls_interp_order and abs_t_interp_order are used to make sure that there are enough points in abs_nls_pert and abs_t_pert for the chosen interpolation order. Note: For homogeneous 1D cases, it can be advantageous to calculate abs_lookup from the 1D atmosphere, and to expand the atmosphere to 3D only after that. This particularly if nonlinear species (i.e., H2O) are involved. See also: abs_lookupSetupBatch

**Authors: **Stefan Buehler

### Synopsis

abs_lookupSetup( | abs_p, abs_t, abs_t_pert, abs_vmrs, abs_nls, abs_nls_pert, atmosphere_dim, p_grid, t_field, vmr_field, atmfields_checked, abs_species, abs_p_interp_order, abs_t_interp_order, abs_nls_interp_order, p_step, t_step, h2o_step ) |

### Variables

OUT | abs_p | (Vector) | List of pressures to be used for the calculation of absorption coefficients. |

OUT | abs_t | (Vector) | List of temperatures to be used for the calculation of absorption coefficients. |

OUT | abs_t_pert | (Vector) | Temperature perturbations for the absorption lookup table. |

OUT | abs_vmrs | (Matrix) | The VMRs (unit: absolute number) on the abs_p grid. |

OUT | abs_nls | (ArrayOfArrayOfSpeciesTag) | Nonlinear species for absorption lookup table generation. |

OUT | abs_nls_pert | (Vector) | Fractional perturbations for the nonlinear species in the absorption lookup table. |

IN | atmosphere_dim | (Index) | The atmospheric dimensionality (1-3). |

IN | p_grid | (Vector) | The pressure grid. |

IN | t_field | (Tensor3) | The field of atmospheric temperatures. |

IN | vmr_field | (Tensor4) | VMR field. |

IN | atmfields_checked | (Index) | OK-flag for atmospheric grids and (physical) fields. |

IN | abs_species | (ArrayOfArrayOfSpeciesTag) | Tag groups for gas absorption. |

IN | abs_p_interp_order | (Index) | The interpolation order to use when interpolating absorption between pressure levels. |

IN | abs_t_interp_order | (Index) | The interpolation order to use when interpolating absorption between the temperature values given by abs_t_pert. |

IN | abs_nls_interp_order | (Index) | The interpolation order to use when interpolating absorption between the H2O values given by abs_nls_pert. |

GIN | p_step | (Numeric, Default: 0.05) | Maximum step in log10(p[Pa]). If the pressure grid is coarser than this, additional points are added until each log step is smaller than this. |

GIN | t_step | (Numeric, Default: 100) | The temperature variation grid step in Kelvin, for a 2D or 3D atmosphere. For a 1D atmosphere this parameter is not used. |

GIN | h2o_step | (Numeric, Default: 100) | The H2O variation grid step [fractional], if H2O variations are done (which is determined automatically, based on abs_species and the atmospheric dimension). For a 1D atmosphere this parameter is not used. |