# ARTS built-in documentation server

## Workspace Method covmat_seAddInverseBlock

### Description

Add the inverse of a block to covariance matrix covmat_se
This functions adds a given matrix as the inverse of a block in the covariance
matrix covmat_se. The purpose of this function is to allow the user to
to use a precomputed inverse for this block in the covariance matrix, that may
for example have been obtained analytically.
This function requires the corresponding non-inverse block to already be present
in covmat_se
If the 'i' and 'j' input arguments are not given, the inverse block
will be added at the position of the most recently added non-inverse diagonal
block.
Note that for this to work this retrieval quantity must be independent from
other retrieval quantities that do not have an inverse. Otherwise the inverse
will be ignored and recomputed numerically.
For the rest, the same requirements as for covmat_seAddBlock apply.

**Authors: **Simon Pfreundschuh

### Synopsis

covmat_seAddInverseBlock( | covmat_se, block, i, j ) |

### Variables

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

GIN | block | (Matrix, Sparse) | The inverse block to add to the covariance matrix |

GIN | i | (Index, Default: -1) | Index of a retrieval quantity. Must satisfy *i* <= *j*. |

GIN | j | (Index, Default: -1) | Index of a retrieval quantity. Must satisfy *i* <= *j*. |