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, so that all four kinds are represented by
four-letter type names.string
. No blanks or double quotation marks (") may
appear inside a word, the former to simplify parsing of an input file
and the latter not to cause conflicts with XML attribute delimiters.
Currently the main application is to store file names.Settings
is associated
with four kinds of information:
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
or a word
(and is not used there), is usually rather
well-defined for a mode
, but less so for a parm
.
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.Settings
class is implemented with the
help of four 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
or <word
are identified, and the information on
such a line is used to define a new flag, mode, parameter or word.
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.
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. 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. 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 = 1.0Each 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.
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.
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 (default = "../xmldoc/Index.xml"
) :
read in the settings from all the files listed in this file, and
assumed to be located in the same subdirectory.
argument
append (default = false
) :
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
os (default = cout
) :
stream for error printout.
argument
startFile (default = "../xmldoc/Index.xml"
) :
read in the settings from all the files listed in this file, and
assumed to be located in the same subdirectory.
argument
os (default = cout
) :
stream for error printout.
Pythia::readString(...)
and
Pythia::readFile(...)
.
argument
line :
the string to be interpreted as an instruction.
argument
warn (default = true
) :
write a warning message or not whenever the instruction does not make
sense, e.g. if the variable does not exist in the databases.
argument
os (default = cout
) :
stream for error printout.
ostream
.
argument
toFile, os :
file or stream on which settings are written.
argument
writeAll (default = false
) :
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).
argument
os (default = cout
) :
output stream for the listing.
void Settings::resetAll() Mode
and
Word
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.
and " "
is returned, respectively.
void Settings::flag(string key, bool now)