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. 
 
 
bool.int.double. The shorthand notation parm is used in the C++ 
code and XML tags.string. No double quotation marks " or braces { } 
may appear inside a word, and commas , will take a special 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 { }.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 { }.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 { }.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 { }.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 { }.{ } 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 
closing brace 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. Finally, it is possible to append to vector 
settings with the notation += { }, similar to the 
+= notation used in Python to append lists. 
 
class:name 
(or file:name, usually these agree), e.g. 
TimeShower:pTmin. The class/file part usually identifies 
the .xml file where the variable is defined, and the part of 
the program where it is used, but such a connection cannot be strictly 
upheld, since e.g. the same variable may be used in a few different 
cases (even if most of them are not).flag, an 
fvec a word or a wvec (and is 
not used there), is usually rather well-defined for a 
mode or mvec, but less so for a 
parm or pvec. Often the allowed range 
exaggerates the degree of our current knowledge, so as not to restrict 
too much what the user can do. One may choose not to set the lower or 
upper limit, in which case the range is open-ended. 
force is 
specified (see below). For modes only, a further boolean 
is stored to specify whether even this should be allowed, or whether 
out-of-range inputs should be forbidden, to the extent that the whole 
PYTHIA initialization should always abort. The latter applies to those 
modes that have been defined with the modepick label in 
the xmldoc/*.xml files, and where maximal and minimal 
values have been specified. Such labels are used to represent a 
discrete set of options, and so any value outside the allowed range is 
just plain wrong. Also attempts to change modefix 
fixed-value modes lead to aborts. By contrast those 
defined with mode or modeopen follow the 
normal rules of being reset to fall into the allowed range, without 
any warnings.Settings class is implemented with the 
help of eight separate maps, one for each kind of variable, with the 
variable name used as key. 
 
 
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. 
.xml files should 
not be changed, except by the PYTHIA authors. Any changes should be 
done with the help of the methods described below. 
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 
 
    pythia.readString(string) 
 
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).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 
 
    pythia.readFile(fileName); 
 
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. It is possible 
to recursively include settings files by the special command 
include = fileName, either in a file or by reading a 
string. An attempt will be made to read fileName, which 
can be either an absolute or relative path. If such a file does not 
exist as an absolute or relative path, then an attempt is made to read 
the file as a relative path from the colon separated list of 
directories optionally specified by setting the 
PYTHIA8CMND environment variable, e.g. export 
PYTHIA8CMND = PATH1:PATH2:.... Finally, if the file is not 
found along these paths the file is searched for relative to the 
directory share/Pythia8/settings, which itself is defined 
relative to the XML path, i.e. xmldoc/... 
 
 
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. 
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. 
 
    pythia.settings.listAll(); 
 
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 
 
    pythia.settings.listChanged(); 
 
where you will only get those variables that differ from their 
defaults. Or you can use 
 
    pythia.settings.list("string"); 
 
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. 
 
    pythia.settings.writeFile(fileName); 
 
This file could then directly be read in by 
readFile(fileName) in a subsequent (identical) run. 
Some variants of this command are listed below. 
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(...). 
 
 Settings::Settings()   argument startFile   : 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. 
   
argument startFile   : 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. 
   
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. 
   
argument match   :  
list all those settings where the name contains 
the match (sub)string (case-insensitive). 
   
   
 
 string Settings::output(string key, bool fullLine = true)   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()   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)   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()   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)   false, 
0, 0., " ", or a 
vector of length 1 and value false, 0, 
0. or " ", respectively, is returned. 
   
 
 bool Settings::flagDefault(string key)   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)   force=false, input values 
outside the allowed range will result in the program failing with 
an error. 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)   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)   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.