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Tutorial: Introduction to Galacticus parameter files
Galacticus parameter files are formatted as XML - a widely used and supported format. Most text editors will recognize XML (providing formatting and highlighting support), and most languages provide tools to work with and manipulate XML files (e.g. the elementTree module in Python).
An extremely simple parameter file (taken from the power spectrum tutorial) might look like:
<?xml version="1.0" encoding="UTF-8"?>
<!-- Parameters for tutorial on computing the power spectrum - https://github.com/galacticusorg/galacticus/wiki/Tutorial%3A-Power-spectra -->
<parameters>
<formatVersion>2</formatVersion>
<version>0.9.4</version>
<!-- Specify tasks to perform -->
<task value="powerSpectra"/>
<!-- Cosmological parameters -->
<cosmologyFunctions value="matterLambda"/>
<cosmologyParameters value="simple">
<HubbleConstant value="70.20000"/>
<OmegaMatter value=" 0.27250"/>
<OmegaDarkEnergy value=" 0.72750"/>
<OmegaBaryon value=" 0.04550"/>
<temperatureCMB value=" 2.72548"/>
</cosmologyParameters>
<!-- Power spectrum options -->
<transferFunction value="eisensteinHu1999">
<neutrinoNumberEffective value="3.046"/>
<neutrinoMassSummed value="0.000"/>
</transferFunction>
<powerSpectrumPrimordial value="powerLaw">
<index value="0.961"/>
<wavenumberReference value="1.000"/>
<running value="0.000"/>
</powerSpectrumPrimordial>
<powerSpectrumPrimordialTransferred value="simple"/>
<cosmologicalMassVariance value="filteredPower">
<sigma_8 value="0.807"/>
<tolerance value="1.0e-3"/>
</cosmologicalMassVariance>
<!-- Structure formation options -->
<linearGrowth value="collisionlessMatter"/>
<!-- Output options -->
<outputFileName value="powerSpectrum.hdf5"/>
<outputTimes value="list">
<redshifts value="0.0 1.0"/>
</outputTimes>
</parameters>The first few lines:
<?xml version="1.0" encoding="UTF-8"?>
<!-- Parameters for tutorial on computing the power spectrum - https://github.com/galacticusorg/galacticus/wiki/Tutorial%3A-Power-spectra -->
<parameters>
<formatVersion>2</formatVersion>
<version>0.9.4</version>contain some header information.
The first line just indicates the XML version and encoding (in general, this never needs to be changed).
The line starting with <!-- and ending with --> is a comment line - you can add comments anywhere in your file to help make it clear what the parameter means, why they were chosen, etc.
This is followed by a line:
<parameters>which marks the start of the actual parameters. This will be matched by a corresponding
</parameters>element at the end of the file.
The remaining two lines in this opening section:
<formatVersion>2</formatVersion>
<version>0.9.4</version>give some useful metadata. They are optional but are usually included. The first, formatVersion, identifies the version of the parameter file format used - it should currently be set to 2 (an older format, version 1, is no longer supported). The second, version, can be used to indicate the version of Galacticus with which this parameter file is intended to be used.
The actual parameters in the file all follow the same structure, for example:
<cosmologyFunctions value="matterLambda"/>
<countTrees value="100" />defines a parameter named "cosmologyFunctions" to have a value of "matterLambda", and a parameter named "countTrees" to have a value of "100".
You can check that your parameter file has correct syntax using the validateParameters.pl script. For example, to run this script on a parameter file named myParameterFile.xml you would do:
./scripts/aux/validateParameters.pl myParameterFile.xml
Any problems with the parameters will be reported. As an example, try running the script on the (intentionally) incorrect parameter file testSuite/parameters/validation/duplicate-value-invalid.xml:
./scripts/aux/validateParameters.pl testSuite/parameters/validation/duplicate-value-invalid.xml
The output should be:
Parameter 'componentSpin' has multiple values
informing you that a parameter appears multiple times in the file.
When you run Galacticus, it checks that your parameter file is correctly formatted, and that it recognizes the parameters that you've included in there - reporting warnings if it finds any problems. These warnings are output in a section beginning:
-> WARNING: problems found with input parameters:
(with WARNING: colored in magenta if supported).
It is recommended to take warnings seriously, and to figure out how to fix your parameter file to remove the warnings. The presence of warnings is often an indicator that your parameter file won't do what you expect it to do.
Warnings of the type:
multiple copies of parameter [componentDisk] present - only the first will be utilized
indicate that the named parameter ("componentDisk" in this case) appears more than once in a section of the parameter file. Most parameters are allowed to appear only once (see here for an explanation of exceptions to this rule). The warning indicates that copies of the parameter after the first are simply being ignored. Often this means that you added a parameter to your file, but forgot to remove the old copy. If the old copy appears first in the file, your new copy will be ignored and you will get unexpected results. The solution is to remove additional copies of the parameter, retaining only the one that you want.
Warnings of the type:
empty value for parameter [cosmologyFunctions]
indicate that the value element of the named parameter ("cosmologyFunctions" in this case) is empty, which is invalid. Either enter a value for the parameter or, if you want the parameter to take its default value (see here) simply remove the parameter from the file entirely.
Warnings of the type:
ambiguous value for parameter [countTrees]
indicate that you have mixed the new and old-styles of parameters, for example:
<countTrees value="10"> <!-- New-style is to define the value via the value attribute here. -->
<value>20</value> <!-- Old-style is to define the value in a separate value element. -->
</countTrees>which leads to an ambiguous choice of value for this parameter. The old-style, while still supported, is deprecated and should not be used, so replace the above with:
<countTrees value="10"/>Warnings of the type:
unrecognized parameter [cosmologyFnuctions] (did you mean [cosmologyFunctions]?)
indicate that the named parameter ("cosmologyFnuctions" in this case) was not recognized as an allowed parameter name. Sometimes this can be due to a typo - Galacticus will try to guess what you actually meany and offer a suggestion if it can. In the above, it guessed that you actually meant "cosmologyFunctions" - correcting this will remove the warning.
The best resource to get information about available parameters, their allowed values, etc. is the Galacticus Physics document. Specifically, the section on Functions section details the available parameters, their types, cardinality, and default values for all allowed classes.
The value must have the correct "type" for each parameter. For example, you can not set a value of "one hundred" for a parameter that expects an integer value. Allowed parameter types are:
- Strings, e.g. "
matterLambda", "starFormation"; - Integers, e.g. "
123", "-45"; - Reals, e.g. "
5.432e-8"; - Booleans, e.g. "
true", "false".
In the Functions section of the documentation a parameter description defines the cardinality, for example, the haloMassFunctionShethTormen class details the following parameters:
Parameters
[a](real; 0,1) {0.707e0} The parameter$a$ in the Sheth et al. [2001] halo mass function fit.
[p](real; 0,1) {0.3e0} The parameter$p$ in the Sheth et al. [2001] halo mass function fit.
[normalization](real; 0,1) {0.3221836349e0} The normalization parameter$A$ in the Sheth et al. [2001] halo mass function fit.
The word "real" (in the "(real; 0,1)") in each of the above parameters indicates that a real type value is expected.
The cardinality of a parameter (i.e. how many values you are allowed to put in the "value" attribute) is typically 1 - i.e. you must provide a single value for the parameter.
Many parameters also allow a cardinality of 0 - corresponding to the case where the parameter simply is not present in the parameter file. In such cases the parameter will be assigned a default value.
Some parameters allow multiple values. For example, in defining a set of output redshifts you might have a parameter:
<redshifts value="0.0 1.0 2.0"/>which has a cardinality of 3, and so defines three output redshifts.
In the Functions section of the documentation a parameter description defines the cardinality, for example, the outputTimesList class details the following parameters:
Parameters
[times](real; 1..*) A list of (space-separated) times at which Galacticus results should be output. Times need not be in any particular order.
[redshifts](real; 0..*) {[0.0e0]} A list of (space-separated) redshifts at which Galacticus results should be output. Redshifts need not be in any particular order.
The cardinality information is given in the parentheses after the parameter name. For the times parameter, the cardinality is 1..\* - indicating that at least one value is required (if the parameter is present at all), and that there is no upper limit to the number of values that can appear.
For the redshifts parameter the cardinality is 0..* - indicating that zero, one, or any number of values can be given. If the redshifts parameter is not present (i.e. there are zero values provided for it) then the default value (given in curly braces in the above) of [0.0e0] will be used instead.
Internally, Galacticus (mostly!) utilizes an object-oriented programming design. You don't need to understand object-oriented programming to use Galacticus, but it can be helpful to appreciate that the content of your parameter file translates directly into the internal objects that Galacticus uses.
Here's a simple example. One class of object used in Galacticus is the cosmologyFunctions class. Here, "class" just means a group of objects which all provide the same functions and interfaces, but which might implement different physics models. As the name implies, the cosmologyFunctions class provides functions related to cosmology (including, for example, the relation between time, cosmologyFunctions class contains three member classes:
-
cosmologyFunctionsMatterLambda: Assumes a universe containing matter and a cosmological constant; -
cosmologyFunctionsMatterDarkEnergy: Assumes a universe containing matter and dark energy with an arbitrary equation of state; -
cosmologyFunctionsStaticUniverse: Assumes a static (non-expanding) universe.
You can find all available classes and members in the Functions section of the documentation.
You can control which member of a class is used by setting the appropriate parameter in your parameter file. For example:
<cosmologyFunctions value="matterLambda"/>would select the cosmologyFunctionsMatterLambda class. Galacticus will build a corresponding cosmologyFunctionsMatterLambda object internally and use it for cosmological calculations.
Many classes require other parameters to configure their behavior. These are specified by setting those parameters inside the parameter selecting the class. For example, the cosmologyFunctionsMatterDarkEnergy class assumes an equation of state darkEnergyEquationOfStateW0 and darkEnergyEquationOfStateW1 respectively. This would be specified as follows:
<cosmologyFunctions value="matterDarkEnergy">
<darkEnergyEquationOfStateW0 value="-1.0"/>
<darkEnergyEquationOfStateW1 value="+0.0"/>
</cosmologyFunctions>Many classes also make use of other classes. For example, the cosmologyFunctionsMatterLambda class requires a helper object of the cosmologyParameters class to provide it with cosmological parameter values (cosmologyParameters class and provide it to the cosmologyFunctions object like this:
<cosmologyFunctions value="matterLambda">
<cosmologyParameters value="simple">
<HubbleConstant value="67.36000"/>
<OmegaMatter value=" 0.31530"/>
<OmegaDarkEnergy value=" 0.68470"/>
<OmegaBaryon value=" 0.04930"/>
<temperatureCMB value=" 2.72548"/>
</cosmologyParameters>
</cosmologyFunctions>When some object is looking for a helper object in the parameter file, the the helper is first looked for inside the object itself - in the above the helper object is cosmologyParameters, and is located inside the cosmologyFunctions object that needs it. If the helper is not found, Galacticus proceeds to look for the helper object at the next higher level in the parameter file. For example in:
<cosmologyParameters value="simple">
<HubbleConstant value="67.36000"/>
<OmegaMatter value=" 0.31530"/>
<OmegaDarkEnergy value=" 0.68470"/>
<OmegaBaryon value=" 0.04930"/>
<temperatureCMB value=" 2.72548"/>
</cosmologyParameters>
<cosmologyFunctions value="matterLambda"/>the cosmologyFunctions object, not finding a helper cosmologyParameters object inside itself, looks outside itself, find the cosmologyParameters object there, and uses it. This is helpful as, for example, many classes need the cosmologyParameters object as a helper - this approach allows us to define it only once and have it be used by many other classes.
If no helper object is found, a default choice is adopted.
Most parameters allow only one copy of the parameter to appear in any given section of the parameter file (and warnings will be issued if multiple copies appear). Some parameters, however, allow multiple copies. Most often, these correspond to classes which sum over the results of other classes (e.g. a cooling function class that sums the cooling rates from multiple other cooling function classes), or applies a sequence of multiple operators.
A common example of this is the nodePropertyExtractor class, which is used to determine which properties to output to the output file. Frequently we want to output many different properties. The nodePropertyExtractorMulti class allows this, for example:
<nodePropertyExtractor value="multi">
<nodePropertyExtractor value="nodeIndices" />
<nodePropertyExtractor value="indicesTree" />
<nodePropertyExtractor value="virialProperties" />
<nodePropertyExtractor value="radiusVelocityMaximum"/>
<nodePropertyExtractor value="velocityMaximum" />
</nodePropertyExtractor>will extract the properties provided by the nodePropertyExtractorNodeIndices, nodePropertyExtractorIndicesTree, nodePropertyExtractorVirialProperties, nodePropertyExtractorRadiusVelocityMaximum, and nodePropertyExtractorVelocityMaximum classes, and concatenate them for output.
All parameters used while running a Galacticus model are written to the output file. This includes parameters set to their default values (and, therefore, did not appear in the original parameter file). Values are stored as attributes in the Parameters group of the output hdf5 file. Nested parameters are stored in a group within the Parameters group, named for their parent parameter.
So, for example, the following parameter file structure:
<cosmologyParameters value="simple">
<HubbleConstant value="70.2 "/>
<OmegaMatter value=" 0.2725 "/>
<OmegaDarkEnergy value=" 0.7275 "/>
<OmegaBaryon value=" 0.0455 "/>
<temperatureCMB value=" 2.72548"/>
</cosmologyParameters>
<cosmologyFunctions value="matterLambda"/>would appear in the output file as:
ATTRIBUTE "cosmologyFunctions" {
DATATYPE H5T_STRING {
STRSIZE 12;
STRPAD H5T_STR_SPACEPAD;
CSET H5T_CSET_ASCII;
CTYPE H5T_C_S1;
}
DATASPACE SCALAR
DATA {
(0): "matterLambda"
}
}
ATTRIBUTE "cosmologyParameters" {
DATATYPE H5T_STRING {
STRSIZE 6;
STRPAD H5T_STR_SPACEPAD;
CSET H5T_CSET_ASCII;
CTYPE H5T_C_S1;
}
DATASPACE SCALAR
DATA {
(0): "simple"
}
}
GROUP "cosmologyFunctions" {
}
GROUP "cosmologyParameters" {
ATTRIBUTE "HubbleConstant" {
DATATYPE H5T_IEEE_F64LE
DATASPACE SCALAR
DATA {
(0): 70.2
}
}
ATTRIBUTE "OmegaBaryon" {
DATATYPE H5T_IEEE_F64LE
DATASPACE SCALAR
DATA {
(0): 0.0455
}
}
ATTRIBUTE "OmegaDarkEnergy" {
DATATYPE H5T_IEEE_F64LE
DATASPACE SCALAR
DATA {
(0): 0.7275
}
}
ATTRIBUTE "OmegaMatter" {
DATATYPE H5T_IEEE_F64LE
DATASPACE SCALAR
DATA {
(0): 0.2725
}
}
ATTRIBUTE "temperatureCMB" {
DATATYPE H5T_IEEE_F64LE
DATASPACE SCALAR
DATA {
(0): 2.72548
}
}
}
Parameter values of type real and cardinality 1 can be written as equations using basic mathematical operations and referencing other (type real, cardinality 1) parameters as variables.
This functionality is provided via libmatheval. This library automatically compiled into the pre-compiled versions of Galacticus. If you compile your own Galacticus then you must have libmatheval available, otherwise math expressions in the parameter file will cause a run-time error.
Math expressions in a parameter are indicated by starting the value element with an =, for example:
<massHalo value="=10.0^13.5/>which would cause the massHalo parameter to evaluate to
Basic mathematical functions are supported - full details are given in the libmatheval documentation.
It is also possible to reference the values of other parameters to use as variable, by enclosing their names in square brackets. For example:
<parameters>
<cosmologyParameters value="simple">
<HubbleConstant value="67.36000"/>
<OmegaMatter value=" 0.31530"/>
<OmegaDarkEnergy value="=1.0-[.::OmegaMatter]"/>
<OmegaBaryon value=" 0.04930"/>
<temperatureCMB value=" 2.72548"/>
</cosmologyParameters>
</parameters>Here, the value of OmegaDarkEnergy is set to equal 1.0 minus the value of OmegaMatter - thereby enforcing a flat universe, i.e.
Multiple levels of the parameter structure can be navigated by separating parameter names by ::.
Paths to parameters can be relative to the location of the current parameter by prefixing the parameter name with .:: as in the above, and you can navigate to higher levels in the parameter hierarchy using ..:: (i.e. . and .. work similarly to their counterparts in the Unix cd command for navigating directories). If neither .:: or ..:: is found at the start of the path, the path is assumed to start from the top of the parameter file.
So, in the above example each of:
OmegaDarkEnergy value="=1.0-[.::OmegaMatter]"/>OmegaDarkEnergy value="=1.0-[cosmologyParameters::OmegaMatter]"/>-
OmegaDarkEnergy value="=1.0-[.::..::cosmologyParameters::OmegaMatter]"/>would achieve the same result (although the last one is a contrived example!).
Sometimes it can be useful to "reuse" an entire section of parameters elsewhere in the parameter file. For example, if you need to create the exact same object more than once, but want to avoid having to update both copies if you decide to change some parameter value. This can be achieved by using parameter IDs and ID references. For example:
<cosmologicalMassVariance value="peackBackgroundSplit">
<cosmologicalMassVariance value="filteredPower" id="myCMV">
<sigma_8 value="0.812"/>
</cosmologicalMassVariance>
</cosmologicalMassVariance>
<mergerTreeBuildController value="constrained">
<mergerTreeBranchingProbabilityUnconstrained value="PCH">
<cosmologicalMassVariance idRef="myCMV"/>
<mergerTreeBranchingProbabilityUnconstrained/>
<mergerTreeBranchingProbabilityConstrained value="gnrlzdPrssSchchtr">
<cosmologicalMassVariance idRef="myCMV"/>
<mergerTreeBranchingProbabilityConstrained/>
</mergerTreeBuildController>In this example, we want to use a peak-background split model for cosmologicalMassVariance and its parameter sigma_8 three times, we add an attribute id="myCMV" to the first instance of the cosmologicalMassVariance parameter. Then, in subsequent cases we can reference it using this ID:
<cosmologicalMassVariance idRef="myCMV"/>This means that, should we decide to change the value of
Note that, internally in Galacticus, these three instances of the cosmologicalMassVariance object are not copies of each other - instead they are the exact same object, reused in these three separate instances.
As described in the Warnings section, Galacticus will emit warnings about any potential problems that it finds in a parameter file. In general, the recommendation is to fix these potential problems!
However, if you are 100% sure that the parameter file is correct and doing what you intended, you can silence the warning for any parameter by adding an attribute ignoreWarnings="true". For example:
<myIntentionallyEmptyParameter value="" ignoreWarnings="true">
<someParameter value="123"/>
</myIntentionallyEmptyParameter>This would normally emit a warning:
MM: -> WARNING: problems found with input parameters:
MM: empty value for parameter [myIntentionallyEmptyParameter]
MM: <-
but with the inclusion of the ignoreWarnings="true" attribute this warning is silenced.
-
Tutorials
- Introduction to Galacticus parameter files
- Dark matter halo mass function
- Warm dark matter halo mass function
- Power spectra
- Warm dark matter power spectra
- Dark matter only merger trees
- Subsampling of merger tree branches
- Dark matter only subhalo evolution
- Solving the excursion set problem
- Reionization calculations
- Instantaneous & Non-instantaneous recycling
- Computing Broadband Stellar Luminosities
- Postprocessing of stellar spectra
- Using N-body Merger Trees
- Generating Mock Catalogs with Lightcones
- Constraining Galacticus parameters
- Generating galaxy merger trees
-
How Galacticus works
- Structure Formation Flowchart
- Merger Tree Building Flowchart
- How Galacticus Evolves Halos and Galaxies
- Galaxy Physics Flowchart
- CGM Cooling Physics Flowchart
- Star Formation Physics Flowchart
- Outflow Physics Flowchart
- Galactic Structure Flowchart
- CGM Physics Flowchart
- SMBH Physics Flowchart
- Subhalo Evolution Flowchart
-
Contributing
- Coding conventions
- Coding tutorials
-
Reference models
- Benchmarks and validation scores
- Validation plots and data