# ARTS built-in documentation server

## Workspace Method propmat_clearskyAddFaraday

### Description

Calculates absorption matrix describing Faraday rotation. Faraday rotation is a change of polarization state of an electromagnetic wave propagating through charged matter by interaction with a magnetic field. Hence, this method requires abs_species to contain 'free_electrons' and electron content field (as part of vmr_field) as well as magnetic field (mag_u_field, mag_v_field, mag_w_field) to be specified. Faraday rotation affects Stokes parameters 2 and 3 (but not intensity!). Therefore, this method requires stokes_dim>2. Like all 'propmat_clearskyAdd*' methods, the method is additive, i.e., does not overwrite the propagation matrix propmat_clearsky, but adds further contributions.

**Authors: **Patrick Eriksson

### Synopsis

propmat_clearskyAddFaraday( | propmat_clearsky, dpropmat_clearsky_dx, stokes_dim, atmosphere_dim, f_grid, abs_species, select_abs_species, jacobian_quantities, rtp_vmr, rtp_los, rtp_mag ) |

### 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 | stokes_dim | (Index) | The dimensionality of the Stokes vector (1-4). |

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

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

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. |

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

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

IN | rtp_los | (Vector) | Line-of-sight at a radiative transfer point. |

IN | rtp_mag | (Vector) | Magnetic field at a radiative transfer point. |