# ARTS built-in documentation server

## Workspace Method retrievalDefInit

### Description

Begin retrieval definition section. This function initialises all variables required for defining retrieval quantities and corresponding covariance matrices. By default, Jacobian quantities should be added withing the. retrieval definition section. If Jacobian quantities are defined separately ``initialize_jacobian`` must be set to 0, otherwise the quantities will be discarded.

**Authors: **Simon Pfreundschuh

### Synopsis

retrievalDefInit( | covmat_se, covmat_sx, covmat_block, covmat_inv_block, jacobian_quantities, jacobian_agenda, initialize_jacobian ) |

### Variables

OUT | covmat_se | (CovarianceMatrix) | Covariance matrix for observation uncertainties. |

OUT | covmat_sx | (CovarianceMatrix) | Covariance matrix of a priori distribution This covariance matrix describes the Gaussian a priori distribution for an OEM retrieval. |

OUT | covmat_block | (Sparse) | Holds matrices used to set blocks in covmat_sx and covmat_se. |

OUT | covmat_inv_block | (Sparse) | Holds matrices used to set the inverse blocks in covmat_sx and covmat_se. |

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

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

GIN | initialize_jacobian | (Index, Default: 1) | Flag whether or not to (re)initialize Jacobian-related quantities. Set to 0 if Jacobian is already defined. |