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Next: The randomize.dat Initialization File Up: XspecManual Previous: Building with the Models   Contents


Adding a Custom Chain Proposal Algorithm

When running a Monte Carlo Markov Chain with the chain command, XSPEC provides several built-in proposal options from which to draw trial parameter values for the next step in the chain. A built-in proposal is selected prior to the chain run with the command: 

chain proposal <distribution> <source>
where <distribution> is the statistical distribution used to randomize the parameter values (e.g. gaussian, cauchy), and <source> refers to the source of the applied covariance information (see the chain command for details).

It is also possible for the user to create an arbitrary new proposal scheme and add it to the options available under the chain proposal command. This is done in a way similar to the adding of local models described in Appendix C, though in this case the code can only be written in C++. Essentially three steps are involved, each described in greater detail below:

  • Create a small text file named randomize.dat.
  • Write a class which inherits from XSPEC's abstract base class RandomizerBase.
  • Run XSPEC's initpackage and lmod commands to build and load the shared library containing the new proposal class(es).


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