Add option to switch between hierarchy and averaging constraints in MP-b...

[mschrode]

...ased tracker alignment

The default behaviour is now to use averaging constraints after
problems with the fit convergence have been found when using
hierarchy constraints. This is explained in more detail in this
presentation by C. Kleinwort,

https://indico.cern.ch/event/337178/session/0/contribution/5/material/slides/0.pdf

Note that the implementation of the averaging constraints is still
approximate for the time being, but adequate for current purposes
and superior to the current version of the hierarchy constraints.

[cmsbuild]

A new Pull Request was created by @mschrode (Matthias Schroeder) for CMSSW_7_3_X.

Add option to switch between hierarchy and averaging constraints in MP-b...

It involves the following packages:

Alignment/CommonAlignmentAlgorithm

@diguida, @cerminar, @cmsbuild, @nclopezo, @rcastello, @mmusich can you please review it and eventually sign? Thanks.
@ghellwig, @pakhotin, @frmeier, @mmusich, @tlampen this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.
@nclopezo, @ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[frmeier]

+1
This solves a convergence issue discovered recently, as mentioned in the presentation linked. Supersedes some manual hot fix. As @mschrode mentioned, this is not the final word but improves the current state. Will have to backport this to other releases.

[cmsbuild]

+1
Tested at: 19d89f2
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6254/715/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6254/715/summary.html

[diguida]

@mschrode @frmeier @mmusich
This PR adds an enum data member for distinguishing between the function minimised in the alignables fit for the MillePede alignment. The current default is set in the config file to be approximate_averaging as the hierarchy constraints method has a problem, introduced by #2370
The approximate average method is currently the most reliable way to run MP.

[diguida]

+1
Based on feedback by @frmeier and @mmusich

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_3_X IBs unless changes (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @nclopezo, @ktf, @smuzaffar

[mschrode]

This PR is still marked as "orp-pending", even though it is "fully merged and closed". Is this a bug of the labeler or is there some information / approval missing? Thx!

[diguida]

@mschrode it is due to the fact that David merged the PR without formally approving it (OTOH he did approve it, as he included it in release).

[mschrode]

@diguida OK I see. Thx for the explanation!