## Main-Program and Related Settings

### 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 number of 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, the `Main:numberToList` mode can be used by you in your main program to decide to list a few of the generated events, whereas `Next:numberListEvent` is used internally in a `pythia.next()` call to do such a listing automatically. Ultimately, in both cases, a `pythia.event.list()` call is the one that generates the listing, explicitly in the main program in the former case, implicitly called from `pythia.next()` in the latter.

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.

The use of several of the `Main:...` options is deprecated in favour of the other possibilities.

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 just send on to the `Settings` ones to do the job, e.g.

      bool   showCS = pythia.flag("Main:showChangedSettings");
      int    nEvent = pythia.mode("Main:numberOfEvents");
      double spare1 = pythia.parm("Main:spareParm1");
      string file   = pythia.word("Main:allSettingsFile");

### Main-program settings

The settings in this section must be under the control of the user, i.e. there are no internal equivalents.

`mode` Main:numberOfEvents (`default = 1000`; `minimum = 0`)
The number of events to be generated.

`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.

### 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.

`flag` Main:showChangedSettings (`default = on`)
Deprecated. Print a list of the changed flag/mode/parameter/word settings.

`flag` Main:showAllSettings (`default = off`)
Deprecated. Print a list of all flag/mode/parameter/word settings. Warning: this will be a long list.

`flag` Main:showChangedParticleData (`default = off`)
Deprecated. Print a list of particle and decay data for those particles that were changed (one way or another).

`flag` Main:showChangedResonanceData (`default = off`)
Deprecated. 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` Main:showAllParticleData (`default = off`)
Deprecated. Print a list of all particle and decay data. Warning: this will be a long list.

`mode` Main:showOneParticleData (`default = 0`; `minimum = 0`)
Deprecated. Print particle and decay data for the particle with this particular identity code. Default means that no particle is printed.

`flag` Main:writeChangedSettings (`default = off`)
Write a file with the changed flag/mode/parameter/word settings, in a format appropriate to be read in at the beginning of a new run, using the `pythia.readFile(fileName)` method.

`word` Main:changedSettingsFile (`default = currentSettings.cmnd`)
The name of the file to which the changed flag/mode/parameter/word settings are written if `Main:writeChangedSettings` is on.

`flag` Main:writeAllSettings (`default = off`)
Write a file with all flag/mode/parameter/word settings, in a format appropriate to be read in at the beginning of a new run, using the `pythia.readFile(fileName)` method.

`word` Main:allSettingsFile (`default = allSettings.cmnd`)
The name of the file to which a flag/mode/parameter/word settings are written if `Main:writeAllSettings` is on.

### 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.

`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.

`mode` Main:numberToList (`default = 2`; `minimum = 0`)
Deprecated. The number of events to list.

`mode` Main:timesToShow (`default = 50`; `minimum = 0`)
Deprecated. Print the number of events generated so far, this many times, i.e. once every `numberOfEvents/numberToShow` events.

### 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.

`flag` Main:showAllStatistics (`default = off`)
Print all available statistics or only the minimal set at the end of the run.

### 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`)