Athena Developer Guide

Athena Chapter 12 N-tuple and Event Collection facilities Version/Issue: 2.0.0
• FUN (optional)
Specifies the name of a function object used for the second-stage preselection. An example of
a such a function object is shown in Listing 12.5. Note that the factory declaration on line 16
is mandatory in order to allow Athena to instantiate the function object.
• The DATAFILE and TYP tags, as well as additional optional tags, have the same meaning
and syntax as for n-tuples, as described in section 12.2.3.1.
Listing 12.5 Example of a function object for second stage pre-selections.
1: class EvtCollectionSelector : public NTuple::Selector {
2: NTuple::Item m_ntrack;
3: public:
4: EvtCollectionSelector(IInterface* svc) : NTuple::Selector(svc) { }
5: virtual ~EvtCollectionSelector() { }
6: /// Initialization
7: virtual StatusCode initialize(NTuple::Tuple* nt) {
8: return nt->item("Ntrack", m_ntrack);
9: }
10: /// Specialized callback for NTuples
11: virtual bool operator()(NTuple::Tuple* nt) {
12: return m_ntrack>cut;
13: }
14: };
15:
16: ObjectFactory EvtCollectionSelectorFactory
12.4 Interactive Analysis using N-tuples
n-tuples are of special interest to the end-user, because they can be accessed using commonly known
tools such as PAW, ROOT or Java Analysis Studio (JAS). In the past it was not a particular strength of
the software used in HEP to plug into many possible persistent data representations. Except for JAS,
only proprietary data formats are understood. For this reason the choice of the output format of the data
depends on the preferred analysis tool/viewer. In the following an overview is given over the possible
data formats.
In the examples below the output of the GaudiExample/NTuple.write program was used.
12.4.1 HBOOK
This data format is used by PAW. PAW can understand this and only this data format. Files of this type
can be converted to the ROOT format using the h2root data conversion program. The use of PAW in
the long term is deprecated.
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