Parameter Features¶
CosmoSIS has several features for modifying the values read from parameter and other files.
Environment Variables¶
Parameter files in CosmoSIS can replace environment variables used in parameter files with their vaules. Use curly brackets like this to do so:
[runtime]
sampler = ${SAMPLER}
In this case the sampler will be chosen depending on the environment variable $SAMPLER.
Variables that are not found in the environment will not be replaced, so you should explicitly set empty values if that is what you want.
Default Parameters & Interpolation¶
Files in the ini format have a standard feature that you can use in CosmoSIS: you can use the values of variables inside other variables. For example, if you have a filename that you use repeatedly through a section, then you can specify it once and re-used it elsewhere.
They also have a special section called DEFAULT whose parameters are available throughout the file. You can combine these like so:
[DEFAULT]
data_directory = path/to/data_file.fits
...
[number_density]
data_file = %(data_directory)s/number_density.fits
...
[likelihood]
data_file = %(data_directory)s/data.fits
Including other parameters files¶
CosmoSIS parameter files can use this command to incorporate another file into their contents:
...
%include path_to_other.ini
...
This has the effect of “pasting” in the other file into the current one.
In general if you use a parameter in an ini file twice the later value will take precedence, so you depending where you put the include directive you can override previous parameters.
The path is looked up relative to the current working directory, not to the first parameter file.
Command Line Overrides¶
It can be useful to override parameters specified in the configuration files on the command line - this can let you launch a variety of different runs with the same file. The -p and -v flags let you override parameters in the main (params.ini) and values files respectively.
You can override any number of parameters in the main parameter file like this:
cosmosis params.ini -p section1.name1=value section2.name2=value ...
For example, this command would change the sampler being used to emcee instead of its current value:
cosmosis params.ini -p runtime.sampler=test
The -v command is used exactly the same way but for the values file, for example, this would change one of the parameter ranges in the pantheon example:
cosmosis examples/pantheon.ini -v cosmological_parameters.omega_m="0.2 0.3 0.5"
Note the quotations marks above, which are needed when there are spaces in the parameter value.