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cosmosis / samplers / star

The Star sampler

Single-component sub-Grid exploration

Name: Star

Version: 1.0

Author(s): CosmoSIS Team




The Star sampler deterministically scans along parameter axes through some central parameter vector: it varies one element of the central parameter vector at a time, scanning along equal incremental shifts in the elementʼs value, from one extreme to the other. The ranges in the values.ini file stipulate the extremes of each parameterʼs range and the central value for that parameter.

As with the grid and test samplers, the outputs can be inspected to reveal the overall shape of the likelihood surface; and here also the shifts along the parameter axes indicate the nature of the directional derivatives in orthogonal directions.


No special installation required; everything is packaged with CosmoSIS


These parameters can be set in the sampler's section in the ini parameter file.
If no default is specified then the parameter is required. A listing of "(empty)" means a blank string is the default.

Parameter Type Meaning Default
nsample_dimension integer The number of equally spaced samples along each dimension (parameter axis). The total number of sample points will thus be this multiplied by the number of variable parameters (the ones with specified ranges in the values.ini file).
nstep Integer The number of samples between each line of output to the results file.
allow_large Boolean An option whose default value of FALSE will prevent the sampler from running if the product of dimensions and nsample_dimension is large; as this sampler is only useful for diagnosing problems with optimization of sample likelihood, excessive computation and output does not generally make sense. Set the option to TRUE to override this fail-safe. FALSE