EDAnalyzers

Overview

Teaching: 7 min
Exercises: 1 min

Questions

• What is an EDAnalyzer and what does it contain?

• What files are relevant in a EDAnalyzer?

Objectives

• Learn what an EDAnalyzer is and how it is structured

• Learn what c++, python and xml files are relevant.

Structure

First, make sure you start up your VM or container like it was discussed in the previous episode.

EDAnalyzers are modules that allow read-only access to the Event. They are useful to produce histograms, reports, statistics, etc. Take a look at the DemoAnalyzer package that we created while validating our CMSSW working environment; it is an example of an EDAnalyzer.

Go to your CMSSW_5_3_32/src area and make sure you issue the cmsenv command (if you are in the same session as the previous episode, there is no need to issue the command again but it never hurts doing it again):

cd <mybasepath>/CMSSW_5_3_32/src
cmsenv

Let’s explore the DemoAnalyzer package:

ls Demo/DemoAnalyzer/

BuildFile.xml  demoanalyzer_cfg.py  doc  interface  python  src  test

ls Demo/DemoAnalyzer/src

DemoAnalyzer.cc

Note that it has a similar structure as any of the CMSSW packages we mentioned before. In this sense, our DemoAnalyzer is just one more CMSSW package. However, the headers and implementation of our simple DemoAnalyzer are coded in one single file under the src directory. The file was automatically named DemoAnalyzer.cc

CMSSW could be very picky about the structure of its packages. Most of the time, scripts or other tools expect to have a Package/Sub-Package structure, just like our Demo/DemoAnalyzer example.

We also notice we have a python configuration file called demoanalyzer_cfg.py (unlike its cousins, it is not inside the python directory). This is the default configurator for the DemoAnalyzer.cc code.

Finally, there is a BuildFile.xml, where we can include any dependencies if needed.

All EDAnalyzers are created equal; of course, if made with the same mkedanlzr, they will look identical. The DemoAnalyzer.cc is a skeleton, written in C++, that contains all the basic ingredients to use CMSSW libraries. So, in order to perform a physics analysis, and extract information from our CMS open data, we just need to understand what to add to this code and how to configure it.

Key Points

• An EDAnalyzer is a an edm class that generates a template for any analysis code using CMSSW.

• There are essentially three important files in an EDAnalyzer package, the source code in c++, the python config file and a Buildfile for tracking dependencies.