 # Difference: SWGuideVertexFitting (17 vs. 18)

#### Revision 182009-02-27 - ThomasSpeer

Line: 1 to 1

 META TOPICPARENT name="SWGuideVertexReco"

# Vertex Fitting

Complete: Line: 15 to 15
The task of the VertexFitter is to control all the steps of the vertex fit from the input of the initial information to the output of the estimated quantities. Depending on the implementation of the concrete VertexFitter, the different objects which perform the different steps are either hard-coded or have to be given at construction time. This page describes all available vertex fitting algorithms.

The fitters can be used easily via the ConfigurableVertexFitter.

>
>

### Usage example

Changed:
<
<
>
>
A simple example of the use of a VertexFitter is given on the WorkBook page. A more detailed description is given here.

Changed:
<
<

## Vertex fitting algorithms

Vertex fitting algorithms can be divided into least-squares algorithms and robust algorithms.

>
>

### Implementation details

Implementation details, are given in the following pages:

Changed:
<
<
In least-squares algorithms all tracks are used, with a weight 1. The KalmanVertexFitter is such a fitter.
>
>

## Vertex fitting algorithms

Changed:
<
<
Robust fitters are able to downweight tracks, and are thus less sensitive to outliers (mismeasured tracks (type 1 outliers) or tracks from another vertex (type 2 outliers)). A common measure of the of the robustness is the break-down point, i.e. the fraction of outliers below which the vertex fit is not affected.
>
>
Vertex fitting algorithms can be divided into least-squares algorithms and robust algorithms. In least-squares algorithms all tracks are used, with a weight 1. The KalmanVertexFitter is such a fitter. Robust fitters are able to downweight tracks, and are thus less sensitive to outliers (mismeasured tracks (type 1 outliers) or tracks from another vertex (type 2 outliers)). A common measure of the of the robustness is the break-down point, i.e. the fraction of outliers below which the vertex fit is not affected.
The fitters now available are:
Changed:
<
<
>
>

## Track refitting after Vertex fit

Copyright &© 2008-2019 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding TWiki? Send feedback