Main-Program and Related Settings
 
  - Introduction
- Initialization settings
- Event-generation settings
- Statistics
- Main-program settings
- Subruns
- Spares
Introduction
 
 
The main program is up to the user to write. However, 
sample main programs 
are provided. In one such class of programs, key settings of the run 
are read in from a "cards file". For experimental collaborations 
this is actually the most common way to run a program like PYTHIA. 
The commands in such a file may be of two types
 
(a) instructions directly to Pythia, like which 
processes to generate, and
 
(b) instructions to the main program for what it should do, 
like how many events to generate, and how many events should 
be listed.
 
In principle these two kinds could be kept completely separate. 
However, to make life simpler, a few useful main-program 
settings are defined on this page, so that they are recognized by 
the Settings machinery. They can thus be put among 
the other cards without distinction. It is up to you to decide which 
ones, if any, you actually want to use when you write your main program. 
 
 
To further reduce the necessary amount of main-program code, some of 
the tasks that you can steer from your main program can also be done 
internally. This in particular relates to some information printing. 
To give an example, pythia.event.list() can be inserted 
to print an event, i.e. all the particles belonging to it. Given the 
length of these listings one would list only a few events at the 
beginning of the run, to get some feeling for the character of events. 
This could be achieved e.g. with a main-program statement
 
   if (iEvent < 3) pythia.event.list()
 
to list the first three events in a loop over iEvent, 
after pythia.next() has been used to generate the next 
event. Alternatively a Next:numberShowEvent = 3 
setting, e.g. in a command file, would achieve the same, by an 
internal call at the end of pythia.next(). 
 
 
The settings names on this page thus fall into four main groups 
 
- Init:...denote actions that automatically may be 
taken during the- pythia.init()call.
- Next:...denote actions that automatically may be 
taken during the- pythia.next()call.
- Stat:...denote actions that automatically may be 
taken during the- pythia.stat()call.
- Main:...denote actions that you yourself 
have the freedom to make use of in your main program.
Initialization settings
 
 
flag   Init:showProcesses   
 (default = on)
Print a list of all processes that will be simulated, with 
their estimated cross section maxima, as used for the 
subsequent Monte Carlo selection. Also print corresponding 
Les Houches initialization data, where relevant. 
   
 
flag   Init:showMultipartonInteractions   
 (default = on)
Print initialization information for the multiparton interactions 
machinery. 
   
 
flag   Init:showChangedSettings   
 (default = on)
Print a list of the changed flag/mode/parameter/word settings. 
   
 
flag   Init:showAllSettings   
 (default = off)
Print a list of all flag/mode/parameter/word settings. 
Warning: this will be a long list. 
   
 
flag   Init:showChangedParticleData   
 (default = on)
Print a list of particle and decay data for those particles 
that were changed (one way or another). 
   
 
flag   Init:showChangedResonanceData   
 (default = off)
In the previous listing also include the resonances that are 
initialized at the beginning of a run and thus get new particle 
data, even if these may well agree with the default ones. 
Warning: this will be a rather long list. 
   
 
flag   Init:showAllParticleData   
 (default = off)
Print a list of all particle and decay data. 
Warning: this will be a long list. 
   
 
mode   Init:showOneParticleData   
 (default = 0; minimum = 0)
Print particle and decay data for the particle with this particular 
identity code. Default means that no particle is printed. 
   
 
wvec   Init:plugins   
 (default = {})
Vector of user provided plugins to load; full details can be found in 
Plugins. Each entry should at a minimum 
take the form LibraryName::ClassName. Here, 
LibraryName is the name of the library, which can include 
an absolute or relative path. If no path is provided, then the 
standard search paths for libraries are searched. The argument 
ClassName specifies the class of the object to load from 
the plugin library. Three additional optional arguments, separated by 
:: can also be provided, 
LibraryName::ClassName::Key::CommandFile::SubRun. For all 
classes except PDFs, Key can be either set, 
which sets the corresponding pointer, or add, which (when 
available) adds to a list of Pythia pointers. For PDF plugins, 
Key specifies the beam type to set. The optional argument 
CommandFile specifies a command file that will be read in 
using the Pythia::readFile method, prior to the 
construction of the plugin object. If SubRun is provided, 
then the settings for only that subrun are read. Warning: none of the 
arguments provided per entry should contain the character 
::, as this is used as a delimeter for the arguments of 
the entry. Additionally, the character , should not be 
used either, as this separates the entries of the vector. All 
arguments are case sensitive. 
   
 
 
Event-generation settings
 
 
mode   Next:numberCount   
 (default = 1000; minimum = 0)
Print a line telling how many events have been generated so far, once 
every numberCount events. If set zero then no lines are 
ever printed. 
In include/Pythia8Plugins/ProgressLog.h an alternative 
method is implemented that intermittently prints out run progress 
information, reports on CPU usage and estimates when the run will end. 
It is used in the main421.cc example. 
   
 
mode   Next:numberShowLHA   
 (default = 1; minimum = 0)
The number of events to list the Les Houches input information for, 
where relevant. 
   
 
mode   Next:numberShowInfo   
 (default = 1; minimum = 0)
The number of events to list the Info information for, 
where relevant. 
   
 
mode   Next:numberShowProcess   
 (default = 1; minimum = 0)
The number of events to list the process record for, 
where relevant. 
   
 
mode   Next:numberShowEvent   
 (default = 1; minimum = 0)
The number of events to list the event record for, 
where relevant. 
   
 
flag   Next:showScaleAndVertex   
 (default = off)
In addition to the normal information in the listing of the 
process and event records, a second line 
per particle provides information on the production scale, 
particle polarization and production vertex. 
   
 
flag   Next:showMothersAndDaughters   
 (default = off)
In addition to the normal information in the listing of the 
process and event records, further lines 
list all the mothers and daughters of each particle. 
   
 
 
Statistics
 
 
flag   Stat:showProcessLevel   
 (default = on)
Print the available statistics on number of generated events and 
cross sections, where relevant. 
   
 
flag   Stat:showPartonLevel   
 (default = off)
Print the available statistics on number and types of multiparton 
interactions, where relevant. 
   
 
flag   Stat:showErrors   
 (default = on)
Print the available statistics on number and types of 
aborts, errors and warnings. 
   
 
flag   Stat:reset   
 (default = off)
Reset the statistics of the above three kinds. The default is that 
all stored statistics information is unaffected by the 
pythia.stat() call. Counters are automatically reset 
in each new pythia.init() call, however, so the only time 
the reset option makes a difference is if stat() 
is called several times in a (sub)run. 
   
 
 
Main-program settings
 
 
The settings in this section must be under the control of the 
user, i.e. there are no internal equivalents. The first one is especially 
important and would be a standard feature of any separate command file. 
 
mode   Main:numberOfEvents   
 (default = 1000; minimum = 0)
The number of events to be generated. 
   
 
mode   Main:numberOfTriedEvents   
 (default = 0; minimum = 0)
The number of events to be tried during generation. Any number smaller 
than one means that the setting will be ignored. 
   
 
mode   Main:numberOfSelectedEvents   
 (default = 0; minimum = 0)
The number of events to be selected during generation. Any number smaller than 
one means that the setting will be ignored. 
   
 
mode   Main:numberOfAcceptedEvents   
 (default = 0; minimum = 0)
The number of events to be accepted during generation. Any number smaller than 
one means that the setting will be ignored. 
   
 
mode   Main:timesAllowErrors   
 (default = 10)
Allow this many times that pythia.next() returns false, 
i.e. that an event is flawed, before aborting the run. 
   
 
 
The Main:... options works like this. Once you have used 
the pythia.readFile(fileName) method to read in the cards 
file, where the values have been set, you can interrogate the 
Settings database to make the values available in your 
main program. A slight complication is that you need to use a different 
Settings method for each of the four possible return types 
that you want to extract. To save some typing the same method names are 
found directly in the Pythia class, and these just send on 
to the Settings ones to do the job, e.g.
 
   int nEvent = pythia.mode("Main:numberOfEvents");  
 
 
The area of subruns is covered separately below. A few spares are also 
defined after that, for unforeseen applications. 
 
 
Subruns
 
 
You can use subruns to carry out 
several tasks in the same run. In that case you will need repeated 
instances of the first setting below in your command file, and could 
additionally use the second and third as well. 
 
mode   Main:subrun   
 (default = -999; minimum = 0)
The number of the current subrun, a non-negative integer, put as 
first line in a section of lines to be read for this particular subrun. 
   
 
flag   Main:LHEFskipInit   
 (default = off)
If you read several Les Houches Event Files that you want to see 
considered as one single combined event sample you can set this flag 
on after the first subrun to skip (most of) the 
(re-)initialization step. 
   
 
mode   Main:numberOfSubruns   
 (default = 0)
The number of subruns you intend to use in your current run. 
Unlike the two settings above, Pythia itself will not 
interpret this number, but you could e.g. have a loop in your main 
program to loop over subruns from 0 through 
numberOfSubruns - 1. 
   
 
 
Spares
 
 
For currently unforeseen purposes, a few dummy settings are made 
available here. The user can set the desired value in a "cards file" 
and then use that value in the main program as desired. 
 
flag   Main:spareFlag1   
 (default = off)
   
 
flag   Main:spareFlag2   
 (default = off)
   
 
flag   Main:spareFlag3   
 (default = off)
   
 
mode   Main:spareMode1   
 (default = 0)
   
 
mode   Main:spareMode2   
 (default = 0)
   
 
mode   Main:spareMode3   
 (default = 0)
   
 
parm   Main:spareParm1   
 (default = 0.)
   
 
parm   Main:spareParm2   
 (default = 0.)
   
 
parm   Main:spareParm3   
 (default = 0.)
   
 
word   Main:spareWord1   
 (default = void)
   
 
word   Main:spareWord2   
 (default = void)
   
 
word   Main:spareWord3   
 (default = void)