blue is hosted by Hepforge, IPPP Durham

LOGO BLUE = Best Linear Unbiased Estimate


This is the homepage of my BLUE project. It contains the up-to-date information about this ROOT implementation of the BLUE combination. Please refer to the latest manual for details on the implementation. For those having access to a computer on which ROOT is installed, the suggested way to run the BLUE package is to follow the section "Hints on the software installation" in the manual.

Usage on computers without a ROOT installation

The ROOT package developed at CERN is available directly as source or binary files, via Github, or as a Docker container. As an example, the workflow when using singularity (see also the Ubuntu package singularity-container) is:

  • singularity -d pull docker://rootproject/root-ubuntu16
  • singularity shell root-ubuntu16.simg

This container has a size of about 570Mb. From here onwards the situation is almost identical to a computer having a ROOT installation. Consequently, again it is suggested to follow the section "Hints on the software installation" of the manual with ROOTSYS=/usr/local/ of the container.

One natural caveat is that the container does not include a LaTeX installation, such that further LaTeX file processing of files generated by the BLUE software need to be performed outside of the container.

For all examples shipped with the BLUE software package (Release 2.3.0), it has been verified that the results obtained with the ROOT Release 6.12/07 of the container agree with those obtained with the present ROOT Pro Release 6.18/04.

License and feedback

The BLUE software package is freely distributed under the GNU Lesser General Public License. It has been written with care, still mistakes are not excluded and it comes without warranty. A number of example functions are provided that reproduce published combination results, and at the same time demonstrate the software usage.

Please inform me should you find mistakes or pecularities. Please give reference to Refs. [1, 2] should you base public results on this software. Should you have any question or suggestion please do not hesitate to send me a message.

Updates are planned on an irregular basis. If you want to be promptly infomed about this via e-mail, please send me a message.


  • 10-Mar-2020: Release 2.4.0
  • 28-Jan-2020: Release 2.3.0
  • 18-Nov-2019: Release 2.2.0
  • 08-Jan-2015: Release 2.1.0
  • 16-Sep-2014: Release 2.0.0
  • 20-May-2014: Release 1.9.2
  • 30-Apr-2014: Release 1.9.1
  • 28-Jan-2014: Release 1.9.0
  • 20-Dec-2013: Release 1.8.0
  • 06-Dec-2013: Release 1.7.0
  • 28-Nov-2013: Release 1.6.0


  • [1] Richard Nisius, BLUE: combining correlated estimates of physics observables within ROOT using the Best Linear Unbiased Estimate method SoftwareX 11 (2020) 100468, DOI: 10.1016/j.softx.2020.100468.
  • [2] Richard Nisius, On the combination of correlated estimates of a physics observable, Eur. Phys. J. C74 (2014) 3004, DOI: 10.1140/epjc/s10052-014-3004-2.

Last Change: 14-Apr-2020 by Richard Nisius.