home.md

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