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# GeneralBrokenLines
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## Introduction
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General Broken Lines are extending the scope of the
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[original broken lines](http://www.desy.de/~blobel/brline.html)
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(or [mirror](http://www.desy.de/~sschmitt/blobel/brline.html)) from a tracking setup
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with a solenoidal magnetic field, independent tracking in and
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perpendicular to the bending plane and multiple scattering in approximated thick
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scatterers to arbitrary propagation of the trajectory, arbitrary measurement planes and
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thick scatterers described by an equivalent pair of thin scatterers.
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A trajectory based on General Broken Lines is a track refit to add the description of
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multiple scattering to an initial trajectory based on the propagation in a magnetic field
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(and average energy loss). It is constructed from a sequence of (pairs of) thin
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scatterers describing the multiple scattering in the material between adjacent
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measurement planes. Predictions for the measurements are obtained by interpolation
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between the enclosing scatterers and triplets of adjacent scatterers define kink angles
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with variance according to the material of the central scatterer. This requires the
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propagation (on the initial trajectory) from a measurement plane or scatterer to the
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previous and next scatterer. The propagation has to be provided by the user in form of
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the jacobians for the local track parameters (transformation matrices). In the case of an
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homogeneous magnetic field they can be calculated from
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[NIM A566:687-698,2006 by A. Strandlie and W. Wittek](https://doi.org/10.1016/j.nima.2006.07.032).
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The initial trajectory can be the result of a fit of the measurements (internal seed) or
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a prediction from another detector part (external seed). A General Broken Lines fit with
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external seed and one (additional) measurement is equivalent to the filtering step of the
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track fit with a Kalman filter.
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As the track refit can provide the complete covariance matrix of **all** track parameters
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General Broken Lines are well suited as track model for calibration and alignment with
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[Millepede II]().
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## Description
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[Draft manual](Gbl_man.pdf)
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## Implementation
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Implementations in Fortran, Python and C++ are provided by DESY under the terms of the
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[LGPLv2 license](http://www.gnu.org/licenses/old-licenses/lgpl-2.0-standalone.html)
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and are maintained in a publicly accessible [GitLab](https://about.gitlab.com)
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[repository at DESY](gitlab.desy.de).
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The recommended version is publicly available via the git command line:
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`git clone --depth 1 --branch V02-04-00
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https://gitlab.desy.de/claus.kleinwort/general-broken-lines.git GBL`
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For development, please clone the repository:
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`git clone https://gitlab.desy.de/claus.kleinwort/general-broken-lines.git GBL`
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The further development is concentrating on the C++ version.
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### Usage
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The usage of the software package is described in corresponding README files. The
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Makefile produces a test executable demonstrating the usage with a simplified track model.
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All versions can directly output the trajectory information to Millepede-II binary files.
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### Documentation
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Online documentation (doxygen) is available for:
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- [Fortran](http://www.desy.de/~kleinwrt/GBL/doc/fortran/html/)
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- [Python](http://www.desy.de/~kleinwrt/GBL/doc/python/html/)
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- [C++](http://www.desy.de/~kleinwrt/GBL/doc/cpp/html/)
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### Remarks
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- The software can be freely used for research and education. We expect that all
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publications describing work using this software quote at least one reference from this
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page.
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- Disclaimer: This software is provided without any expressed or implied warranty. In
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particular there is no warranty of any kind concerning the fitness of this software for
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any particular purpose.
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## [Version history](history)
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## Contact
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For questions, suggestions or help please contact: Claus(dot)Kleinwort(at)desy(dot)de
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## References
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- Fast alignment of a complex tracking detector using advanced track models, Volker
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Blobel, Claus Kleinwort, Frank Meier, Computer Phys. Communications (2011),
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[doi:10.1016/j.cpc.2011.03.017](http://dx.doi.org/10.1016/j.cpc.2011.03.017)
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- General Broken Lines as advanced track fitting method, Claus Kleinwort, NIM A, 673
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(2012), 107-110, [doi:10.1016/j.nima.2012.01.024](http://dx.doi.org/10.1016/j.nima.2012.01.024)
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