3 <title>Event Statistics</title>
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30 <h2>Event Statistics</h2>
32 At the end of the run you will want to write out the final statistics
33 on number of events generated, the corresponding cross sections and
34 the number of errors encountered. This is done either with the
35 <code>pythia.stat()</code> method or the <code>pythia.statistics()</code>
36 one, assuming <code>pythia</code> is an instance of the
37 <code>Pythia</code> class.The former method is steered entirely by
38 settings values, see <?php $filepath = $_GET["filepath"];
39 echo "<a href='MainProgramSettings.php?filepath=".$filepath."' target='page'>";?>here</a>.
40 The latter, deprecated one instead takes two arguments:
42 <a name="method1"></a>
43 <p/><strong>void Pythia::statistics(bool all = false, bool reset = false) </strong> <br/>
44 write out statistics on cross sections and errors. This is based on
45 calls to the methods below, for the two kinds of information.
46 <br/><code>argument</code><strong> all </strong> :
47 if <code>true</code> it allows a more extensive listing than the default
48 one, see multiparton-interactions statistics below.
50 <br/><code>argument</code><strong> reset </strong> : if <code>true</code> it implies that all counters,
51 e.g on events generated and errors experienced, are reset to zero whenever
52 the routine is called. The default instead is that all stored
53 statistics information is unaffected by the call.
54 Counters are automatically reset in each new <code>Pythia::init()</code>
55 call, however, so the only time the <code>reset</code> option makes a
56 difference is if <code>statistics(...)</code> is called several times
61 <h3>Cross-section statistics</h3>
63 The <code>ProcessLevel::statistics()</code> method cannot be accessed
64 directly, but only via the <code>Pythia::stat()</code> and
65 <code>Pythia::statistics(...)</code> calls above.
66 When called it will loop over the list of existing processes, and for
67 each write out name, code, the number of tried, selected and accepted
68 events, the cross section and the estimated error on the latter.
69 The three different event numbers are related to the Monte Carlo method
70 used, whereby an initial upper estimate of the cross section is used to
71 select a large number of trial phase-space points, whereof then not all
72 survive. Rejections are normally done by the internal machinery, but can
73 also be obtained by <?php $filepath = $_GET["filepath"];
74 echo "<a href='UserHooks.php?filepath=".$filepath."' target='page'>";?>user hooks</a>.
77 <li><b>tried</b> events reflect the original number of
78 phase-space points probed, as part of the upper estimate;</li>
79 <li><b>selected</b> events correspond to those that survive
80 the internal Monte-Carlo selection procedure;</li>
81 <li><b>accepted</b> events are those that also survive
82 the additional user cuts.</li>
84 In most runs there would be no user hooks implemented, and then the
85 numbers of selected and of accepted events will agree. Aborted events
86 (see below) usually appear in the selected statistics but not in the
90 For Les Houches events the total cross section will be correctly
91 displayed; however the (optional) error value will not be used, so that
92 the reported error will be smaller than the correct statistical ones,
93 and often vanish completely. Furthermore, while the number of events
94 is shown for each user process, the cross section is only for the sum
97 <h3>Error messages</h3>
99 When Pythia is run, errors may occur, and give rise to warning messages.
100 These may be of varying severity, as follows:
102 <li><b>Abort</b> means things went seriously wrong, and the
103 initialization or event generation failed. In the former case it is
104 not possible to generate events at all, in the latter the current
105 event is flawed and should be skipped. In either case the respective
106 method, <code>Pythia::init()</code> or <code>Pythia::next()</code>,
107 then also returns the value <code>false</code>. There are occasions
108 where an abort may be deliberate, such as when a file of Les Houches
109 Events is read and the end of the file is reached.</li>
110 <li><b>Error</b> normally is less severe. Typically the program will
111 back up one step and try again. There are cases where this is not possible,
112 in particular during the initialization and the generation of a hard
113 process, and then the error may be followed by an abort as a direct
114 consequence (with two separate messages).</li>
115 <li><b>Warning</b> is even less severe. In some cases the program will
116 try again, with good chances of success, in others no measure at all
117 need to be taken.</li>
121 The error messages is handled by a small part of the <code>Info</code>
122 class. It is handed any abort, error or warning messages during the event
123 generation phase, and will store each distinct message, with a counter
124 for how many times it is issued. Thus it is possible to limit the number
125 of identical messages issued, currently hardcoded so that each kind of
126 error message is only printed once
127 (<code>static const int TIMESTOPRINT = 1</code>).
128 This can be overridden by the calling routine, so that all messages of
129 this kind are shown, which is particularly relevant for the
130 initialization stage.
131 The summary table printed by <code>Pythia::statistics()</code>
132 provides a table with all the different messages issued, in
133 alphabetical order, with the total number of times each was generated.
135 <h3>Multiparton-interactions statistics</h3>
137 If you call <code>Pythia::statistics(true)</code>, i.e. with the first
138 optional argument <code>true</code>, also statistics on multiparton
139 interactions is printed, comprising a list of all allowed subprocesses
140 with how many times each of them has been generated. For the minimum-bias
141 process this also includes the hardest interaction, while else the
142 hardest process is excluded from the statistics. (This is because
143 the hardest process is of the same character and generated by the same
144 machinery in the former case but not in the latter. Also, for the
145 former case only, the standard statistics listing only lists
146 minimum bias as one single process, i.e. does not further specify
147 the character of the hardest subprocess, so there is not any overlap
153 <!-- Copyright (C) 2013 Torbjorn Sjostrand -->