# ARTS built-in documentation server

## Workspace Method propmat_clearskyAddFromLookup

### Description

Extract gas absorption coefficients from lookup table. This extracts the absorption coefficient for all species from the lookup table, and adds them to the propagation matrix. Extraction is for one specific atmospheric condition, i.e., a set of pressure, temperature, and VMR values. Some special species are ignored, for example Zeeman species and free electrons, since their absorption properties are not simple scalars and cannot be handled by the lookup table. The interpolation order in T and H2O is given by abs_t_interp_order and abs_nls_interp_order, respectively. Extraction is done for the frequencies in f_grid. Frequency interpolation is controlled by abs_f_interp_order. If this is zero, then f_grid must either be the same as the internal frequency grid of the lookup table (for efficiency reasons, only the first and last element of f_grid are checked), or must have only a single element. If abs_f_interp_order is above zero, then frequency is interpolated along with the other interpolation dimensions. This is useful for calculations with Doppler shift. For Doppler calculations, you should generate the table with a somewhat larger frequency grid than the calculation itself has, since the Doppler shift will push the frequency grid out of the table range on one side. Some extrapolation is allowed. For pressure and frequency interpolation the standard extrapolation factor of 0.5 is applied. The factor is the default for temperature and VMR interpolation, but the extrapolation limit can here be adjusted by the *extpolfac* argument.

**Authors: **Stefan Buehler, Richard Larsson

### Synopsis

propmat_clearskyAddFromLookup( | propmat_clearsky, dpropmat_clearsky_dx, abs_lookup, abs_lookup_is_adapted, abs_p_interp_order, abs_t_interp_order, abs_nls_interp_order, abs_f_interp_order, f_grid, rtp_pressure, rtp_temperature, rtp_vmr, jacobian_quantities, abs_species, select_abs_species, extpolfac, no_negatives ) |

### Variables

OUT+IN | propmat_clearsky | (PropagationMatrix) | This contains the absorption coefficients for one point in the atmosphere (one set of pressure, temperature, magnetic field, and VMR values). |

OUT+IN | dpropmat_clearsky_dx | (ArrayOfPropagationMatrix) | Partial derivative of absorption coefficients. |

IN | abs_lookup | (GasAbsLookup) | An absorption lookup table. |

IN | abs_lookup_is_adapted | (Index) | Flag to indicate whether abs_lookupAdapt has already been called. |

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. |

IN | abs_f_interp_order | (Index) | Frequency interpolation order for absorption lookup table. |

IN | f_grid | (Vector) | The frequency grid for monochromatic pencil beam calculations. |

IN | rtp_pressure | (Numeric) | Pressure at a radiative transfer point. |

IN | rtp_temperature | (Numeric) | Temperature at a radiative transfer point. |

IN | rtp_vmr | (Vector) | Absorption species abundances for radiative transfer calculations. |

IN | jacobian_quantities | (ArrayOfRetrievalQuantity) | The retrieval quantities in the Jacobian matrix. |

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

IN | select_abs_species | (ArrayOfSpeciesTag) | A select species tag group from abs_species If set to empty, this selection is void. |

GIN | extpolfac | (Numeric, Default: 0.5) | Extrapolation factor (for temperature and VMR grid edges). |

GIN | no_negatives | (Index, Default: 1) | Boolean. If it is true negative values due to interpolation are set to zero. |