Settings Scheme

  1. Concepts
  2. Operation
  3. The public methods
The Settings class keeps track of all the flags, modes, parameters and words used during the event generation. As such, it serves all the Pythia program elements from one central repository. Accessing it allows the user to modify the generator behaviour.

Each Pythia object has a public member settings of the Settings class. Therefore you access the settings methods as pythia.settings.command(argument), assuming that pythia is an instance of the Pythia class. Further, for the most frequent user tasks, Pythia methods have been defined, so that pythia.command(argument) would work, see further below.

The central section on this page is the Operation one. The preceding concepts section is there mainly to introduce the basic structure and the set of properties that can be accessed. The subsequent sections provide a complete listing of the existing public methods, which most users probably will have little interaction with.


We distinguish eight kinds of user-modifiable variables, by the way they have to be stored:
  1. Flags are on/off switches, and are stored as bool.
  2. Modes corresponds to a finite enumeration of separate options, and are stored as int.
  3. Parameters take a continuum of values, and are stored as double. The shorthand notation parm is used in the C++ code and XML tags.
  4. Words are simple character strings and are stored as string. No double quotation marks " or braces { } may appear inside a word, and commas , will take a spcial role next so should also be avoided. Normally the input string is expected not to contain any blanks or equal signs, but if it does it must be enclosed in braces { }.
  5. Vectors of flags take a variable length, and are stored as vector<bool>. The shorthand notation fvec is used in the C++ code and XML tags. When the vector is input as a string it should be given as a comma-separated list, either containing no blanks or else enclosed in braces { }.
  6. Vectors of modes take a variable length, and are stored as vector<int>. The shorthand notation mvec is used in the C++ code and XML tags. When the vector is input as a string it should be given as a comma-separated list, either containing no blanks or else enclosed in braces { }.
  7. Vectors of parameters take a variable length and for each element a continuum of values, and are stored as vector<double>. The shorthand notation pvec is used in the C++ code and XML tag. When the vector is input as a string it should be given as a comma-separated list, either containing no blanks or else enclosed in braces { }.
  8. Vectors of words take a variable length, and are stored as vector<string>. The shorthand notation wvec is used in the C++ code and XML tags. When the vector is input as a string it should be given as a comma-separated list, either containing no blanks or else enclosed in braces { }.
Note the special role played by the braces { } to enclose words or lists that are allowed to contain blanks and equal signs, and of commas , to separate the fields of the list, in analogy with how C++ arrays can be initialized. You should not be using these three characters for any other purposes. Input of a vector can be split across several lines, until a close brace } is found that matches the open brace {. If no such is found the program will abort, so beware. The double quotation mark " is avoided since it is already used for other purposes. Also note that all shorthands have been chosen four letters long.

In general, each variable stored in Settings is associated with four kinds of information:

Technically, the Settings class is implemented with the help of eight separate maps, one for each kind of variable, with the variable name used as key.


The normal flow of setting values is:

  1. When a Pythia object pythia is created, the member pythia.settings is asked to scan the files listed in the Index.xml file in the xmldoc subdirectory.

    In all of the files scanned, lines beginning with <flag, <mode, <parm, <word, <fvec, <mvec, <pvec or <wvec are identified, and the information on such a line is used to define a new flag, mode, parameter, word, or vector of flags, modes or parameters. To exemplify, consider a line

    <parm name="TimeShower:pTmin" default="0.5" min="0.1" max="2.0"> 
    which appears in the TimeShower.xml file, and there defines a parameter TimeShower:pTmin with default value 0.5 GeV and allowed variation in the range 0.1 - 2.0 GeV. The min and max values are optional.
    Important: the values in the .xml files should not be changed, except by the PYTHIA authors. Any changes should be done with the help of the methods described below.
  2. Between the creation of the Pythia object and the init call for it, you may use several alternative methods to modify some of the default values. The same variable can be changed several times. If so, it is the last read value that counts. The two special Tune:ee and Tune:pp modes and the Print:quiet flag are expanded to change several settings in one go, but these obey the same ordering rules.

    a) Inside your main program you can directly set values with

    where both the variable name and the value are contained inside the character string, separated by blanks and/or a =, e.g.
        pythia.readString("TimeShower:pTmin = 1.0"); 
    The match of the name to the database is case-insensitive. Names that do not match an existing variable are ignored. A warning is printed, however. Strings beginning with a non-alphanumeric character, like # or !, are assumed to be comments and are not processed at all. Values below the minimum or above the maximum are set at the respective border. In extreme cases, where it is necessary to go outside the allowed range, "FORCE=" can replace the normal "=" separator to force the requested value, at own responsibility. For bool values, the following notation may be used interchangeably: true = on = yes = ok = 1, while everything else gives false (including but not limited to false, off, no and 0).

    b) The Pythia readString(string) method actually does not do changes itself, but sends on the string either to the Settings class or to ParticleData. The former holds if the string begins with a letter, the latter if it begins with a digit. (The exception is if an input list has been begun by an open brace { but no matching close brace } was present; then all subsequent non-empty input is directed to Settings until the close brace is found.) If desired, it is possible to communicate directly with the corresponding Settings method:

        pythia.settings.readString("TimeShower:pTmin = 1.0"); 
    In this case, changes intended for ParticleData would not be understood.

    c) Underlying the settings.readString(string) method are the settings-type-sensitive commands in the Settings, that are split by names containing flag, mode, parm or word. Thus, the example now reads

        pythia.settings.parm("TimeShower:pTmin", 1.0); 
    Such a form could be convenient e.g. if a parameter is calculated at the beginning of the main program, and thus is available as a variable rather than as a character string. Note that Boolean values must here be given as true or false i.e. there is less flexibility than with the previous methods.

    At the same level, there are several different methods available. These are included in the full description below, but normally the user should have no need for them.

    d) A simpler and more useful way is to collect all your changes in a separate file, with one line per change, e.g.

        TimeShower:pTmin = 1.0 
    Each line is read in as a string and processed with the methods already introduced. The file can be read by the
    method (or an istream instead of a fileName). The file can freely mix commands to the Settings and ParticleData classes, and so is preferable. Lines with settings are handled by calls to the pythia.settings.readString(string) method.

    A file can make use of two extra features that are not available with the readString(...) method. One is the possibility to provide information for several distinct subruns. The other is the possibility to comment out a section of lines in the file. The first line of the commented section should then begin by /* and the last begin by */. This is reminiscent of the convention used in C++ and other languages, but is not as powerful, in that it is not possible to comment in or out parts of lines. It is only the first two non-blank characters of a line that are checked for a match, and a line beginning with */ is counted as part of the commented section. To avoid mistakes it is best to keep /* and */ on lines of their own, optionally followed by comments, but not by commands.

  3. In the pythia.init() call, many of the various other program elements are initialized, making use of the current values in the database. Once initialized, the common Settings database is likely not consulted again by these routines. It is therefore not productive to do further changes in mid-run: at best nothing changes, at worst you may set up inconsistencies.

    A routine reInit(fileName) is provided, and can be used to zero all the maps and reinitialize them from scratch. Such a call might be useful if several subruns are to be made with widely different parameter sets - normally the maps are only built from scratch once, namely when the Pythia() object is created. A more economical alternative is offered by resetAll(), however, which sets all variables back to their default values.

  4. You may at any time obtain a listing of all variables in the database by calling
    The listing is strictly alphabetical, which at least means that names from the same file are kept together, but otherwise may not be so well-structured: important and unimportant ones will appear mixed. A more relevant alternative is
    where you will only get those variables that differ from their defaults. Or you can use
    where only those variables with names that contain the string (case-insensitive match) are listed. Thus, with a string shower, the shower-related variables would be shown.

    The method pythia.settings.output(key) can return the value of a variable as a string, convenient for output. In a readString or readFile command, the construction key = ? will echo back the variable and its value, using this method.

  5. The above listings are in a tabular form that cannot be read back in. Assuming you want to save all changed settings (maybe because you read in changes from several files), you can do that by calling
    This file could then directly be read in by readFile(fileName) in a subsequent (identical) run. Some variants of this command are listed below.

The public methods

The complete list of methods and arguments is as follows. Most of the ones of interest to the user have already been mentioned above. Others can be used, but the same functionality is better achieved by higher-level routines. Some are part of the internal machinery, and should not be touched by user.

Note that there is no Settings::readFile(...) method. The intention is that you should use Pythia::readFile(...). It parses and decides which individual lines should be sent on to Settings::readString(...).

the constructor, which takes no arguments. Internal.

bool Settings::initPtr(Info* infoPtrIn)  
initialize pointer to error-message database. Internal.

bool Settings::init(string startFile = "../share/Pythia8/xmldoc/Index.xml", bool append = false)  
read in the settings database.
argument startFile : read in the settings from all the files listed in this file, and assumed to be located in the same subdirectory.
argument append (default = off) : By default nothing is done if the method has already been called once. If true the further settings read in are added to the current database.
Note: The method returns false if it fails.

bool init(istream& is, bool append = false)  
read in the settings from an input stream. This allows initialization without reading the xml files directly, which is useful for initialization of multiple copies of Pythia8.

bool Settings::reInit(string startFile = "../share/Pythia8/xmldoc/Index.xml")  
overwrite the existing database.
argument startFile : read in the settings from all the files listed in this file, and assumed to be located in the same subdirectory.
Note: The method returns false if it fails.

bool Settings::readString(string line, bool warn = true)  
read in a string, and change the relevant quantity in the database. It is normally used indirectly, via Pythia::readString(...) and Pythia::readFile(...).
argument line : the string to be interpreted as an instruction.
argument warn (default = on) : write a warning message or not whenever the instruction does not make sense, e.g. if the variable does not exist in the databases.
Note: the method returns false if it fails to make sense out of the input string.

bool Settings::writeFile(string toFile, bool writeAll = false)  
bool Settings::writeFile(ostream& os = cout, bool writeAll = false)  
write current settings to a file or to an ostream.
argument toFile, os : file or stream on which settings are written.
argument writeAll (default = off) : normally only settings that have been changed are written, but if true then all settings are output.
Note: the method returns false if it fails.

bool Settings::writeFileXML(ostream& os = cout)  
write out the information stored in xmldoc to be used later to initialize Settings through an input stream.

void Settings::listAll()  
void Settings::listChanged()  
void Settings::list(string match)  
list all or changed settings, or a group of them.
argument match : list all those settings where the name contains the match (sub)string (case-insensitive).

string Settings::output(string key, bool fullLine = true)  
provide the value of a variable as a character string, whatever the type. If the variable does not exist then unknown is returned.
argument key : the name of the settings variable.
argument fullLine (default = on) : If true then a whole "line" is returned, " key = value\n", while if false only the value string.

vector<string> Settings::getReadHistory()  
Method to retrieve the history of readString commands that have been processed by the Settings instance, e.g. for inspection. Note that readFile command lines are interpreted by readString and thus also are listed, as are the Settings commands read by Pythia::readString and Pythia::readFile.

vector<string> Settings::getReadHistory(int subrun)  
Method to retrieve the history of readString commands that have been processed by Settings, for a specific subrun (see the section on Main-Program Settings). For subrun = -1, returns the readString history common to all subruns. For subrun >= 0, returns the history of readString commands for that specific subrun (omitting the common part).

void Settings::resetAll()  
reset all current values to their defaults.

bool Settings::isFlag(string key)  
bool Settings::isMode(string key)  
bool Settings::isParm(string key)  
bool Settings::isWord(string key)  
bool Settings::isFVec(string key)  
bool Settings::isMVec(string key)  
bool Settings::isPVec(string key)  
bool Settings::isWVec(string key)  
return true if an entry of the given name and kind exists, else false.

void Settings::addFlag(string key, bool default)  
void Settings::addMode(string key, int default, bool hasMin, bool hasMax, int min, int max)  
void Settings::addParm(string key, double default, bool hasMin, bool hasMax, double min, double max)  
void Settings::addWord(string key, string default)  
void Settings::addFVec(string key, vector<bool> default)  
void Settings::addMVec(string key, vector<int> default, bool hasMin, bool hasMax, int min, int max)  
void Settings::addPVec(string key, vector<double> default, bool hasMin, bool hasMax, double min, double max)  
void Settings::addWVec(string key, vector<string> default)  
add an entry of the respective kind to the database. The name and default value(s) always has to be supplied, for Mode, Parm, MVec and PVec additionally if lower and/or upper limits are to be imposed and, if so, what those limit are.

bool Settings::flag(string key)  
int Settings::mode(string key)  
double Settings::parm(string key)  
string Settings::word(string key)  
vector<bool> Settings::fvec(string key)  
vector<int> Settings::mvec(string key)  
vector<double> Settings::pvec(string key)  
vector<string> Settings::wvec(string key)  
return the current value(s) of the respective setting. If the name does not exist in the database, a value false, 0, 0., " ", or a vector of length 1 and value false, 0, 0. or " ", respectively, is returned.

bool Settings::flagDefault(string key)  
int Settings::modeDefault(string key)  
double Settings::parmDefault(string key)  
string Settings::wordDefault(string key)  
vector<bool> Settings::fvecDefault(string key)  
vector<int> Settings::mvecDefault(string key)  
vector<double> Settings::pvecDefault(string key)  
vector<string> Settings::wvecDefault(string key)  
return the default value(s) of the respective setting. If the name does not exist in the database, a value false, 0, 0., " ", or a vector of length 1 and value false, 0, 0. or " ", respectively, is returned.

map<string, Flag> Settings::getFlagMap(string match)  
map<string, Mode> Settings::getModeMap(string match)  
map<string, Parm> Settings::getParmMap(string match)  
map<string, Word> Settings::getWordMap(string match)  
map<string, FVec> Settings::getFVecMap(string match)  
map<string, MVec> Settings::getMVecMap(string match)  
map<string, PVec> Settings::getPVecMap(string match)  
map<string, WVec> Settings::getWVecMap(string match)  
return a map of all settings of the respective type that contain the string "match" in its name.

void Settings::flag(string key, bool now, bool force = false)  
void Settings::mode(string key, int now, bool force = false)  
void Settings::parm(string key, double now, bool force = false)  
void Settings::word(string key, string now, bool force = false)  
void Settings::fvec(string key, vector<bool> now, bool force = false)  
void Settings::mvec(string key, vector<int> now, bool force = false)  
void Settings::pvec(string key, vector<double> now, bool force = false)  
void Settings::wvec(string key, vector<string> now, bool force = false)  
change the current value(s) of the respective setting to the provided new value(s). If lower or upper limits have been set and force=false, input values outside the allowed range are reinterpreted as being at the nearest limit. If force = true, upper and lower limits will be ignored, allowing to force values outside the allowed range (to be used with caution and at own responsibility!). Any key not found in the settings database will be ignored, unless force = true, in which case the missing key will be added to the database with the given value.

void Settings::forceMode(string key, int now)  
void Settings::forceParm(string key, double now)  
void Settings::forceMVec(string key, vector<int> now)  
void Settings::forcePVec(string key, vector<double> now)  
as above, but do not check lower and upper limits, so that the current value(s) can be put outside the intended borders.
Note: these methods have been superseded by the force = true option in the standard methods above. They are kept for backwards compatibility with version 8.223 and earlier but will be removed in a future major release.

void Settings::resetFlag(string key)  
void Settings::resetMode(string key)  
void Settings::resetParm(string key)  
void Settings::resetWord(string key)  
void Settings::resetFVec(string key)  
void Settings::resetMVec(string key)  
void Settings::resetPVec(string key)  
void Settings::resetWVec(string key)  
reset the current value to the default one.

bool Settings::getIsInit()  
return true if the database has been initialized, else false.

bool Settings::readingFailed()  
return true if some input could not be parsed, else false.

bool Settings::unfinishedInput()  
return true if input of a vector has been begun with am open brace { but no matching closing brace } has been found (so far), else false.

bool Settings::hasHardProc()  
return true if any hard processes are switched on, i.e. any process not belonging to the SoftQCD or LowEnergyQCD categories, else false. This method does not check whether Les Houches input is used, so that may have to be done separately. Since the method contains a hardcoding of what hard process types exist, in order to detect if any are on, it could be broken by the addition of new internal processes. It is therefore mainly useful for warning purposes, not for hard decisions.