# ARTS built-in documentation server

## Workspace Method jacobianAddPolyfit

### Description

Includes polynomial baseline fit in the Jacobian. This method deals with retrieval of disturbances of the spectra that can be described by an additive term, a baseline off-set. The baseline off-set is here modelled as a polynomial. The polynomial spans the complete frequency range spanned by sensor_response_f_grid and the method should only of interest for cases with no frequency gap in the spectra. The default assumption is that the off-set differs between all spectra, but it can also be assumed that the off-set is common for all e.g. line-of-sights. If the simulation/retrieval deals with a single spectrum, the number of elements added to the state vector (x) is poly_order+1. The coefficient for polynomial order 0 comes first etc. The same is true if ``no_pol_variation``, ``no_los_variation`` and ``no_mblock_variation`` all are set to 1, even if several spectra are involved. Otherwise thenumber of elements added to x depends on the number of spectra and the settings of ``no_pol_variation``, ``no_los_variation`` and ``no_mblock_variation``. The coefficients of the different polynomial orders are treated as separate retrieval quantities. That is, the the elements associated with polynomial order 0 are grouped and form together a retrieval quantity. The coefficients for higher polynomial orders are treated in the same way.

**Authors: **Patrick Eriksson

### Synopsis

jacobianAddPolyfit( | jacobian_quantities, jacobian_agenda, sensor_response_pol_grid, sensor_response_dlos_grid, sensor_pos, poly_order, no_pol_variation, no_los_variation, no_mblock_variation ) |

### Variables

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

OUT+IN | jacobian_agenda | (Agenda) | Pure numerical Jacobian calculations. |

IN | sensor_response_pol_grid | (ArrayOfIndex) | The "polarisation grid" associated with sensor_response. |

IN | sensor_response_dlos_grid | (Matrix) | The zenith and azimuth angles associated with sensor_response. |

IN | sensor_pos | (Matrix) | The sensor position for each measurement block. |

GIN | poly_order | (Index) | Polynomial order to use for the fit. |

GIN | no_pol_variation | (Index, Default: 0) | Set to 1 if the baseline off-set is the same for all Stokes components. |

GIN | no_los_variation | (Index, Default: 0) | Set to 1 if the baseline off-set is the same for all line-of-sights (inside each measurement block). |

GIN | no_mblock_variation | (Index, Default: 0) | Set to 1 if the baseline off-set is the same for all measurement blocks. |