bayes: set up for Bayesian inference

Syntax:           bayes [<option> | <mod par #>] {<prior type> <hyperparameters>}

where <opton> =:: [off | on | cons]. If a parameter number is given as the first argument then this command sets up the prior for the specified model parameter. The supported priors are `cons' and `exp'. The cons prior requires no hyperparameters and the exp prior requires a hyperparameter giving the exponential decay scale. The log prior for the exp case is taken to be -param/hparam - log(hparam), where param is the fit parameter value and hparam the hyperparameter. If the first argument to the `bayes' command is not a parameter number then one of the options ‘off’, ‘on’, ‘cons’ is used.  The first two turn Bayesian inference off or on, while ‘cons’ turns Bayesian inference on and gives all parameters a constant prior.