;+
; NAME:
;   hogg_mcmc_step
; PURPOSE:
;   Make one step in a Markov Chain Monte Carlo.
; INPUTS:
;   seed       - random number seed for randomu()
;   pars       - initial parameters (can be an array or structure)
;   like       - initial likelihood
;   step_func  - function that takes a step in parameter space
;   like_func  - function that computes the likelihood
; OUTPUTS:
;   newpars    - new parameters
;   newlike    - new likelihood
; BUGS:
;   - I made up the algorithm based on things I sort-of remember.
; REVISION HISTORY:
;   2005-03-31  started - Hogg
;-
pro hogg_mcmc_step, seed,pars,like,step_func,like_func,newpars,newlike
if (NOT keyword_set(like)) then like= call_function(like_func,pars)
repeat begin
    newpars= call_function(step_func,seed,pars)
    newlike= call_function(like_func,newpars)
endrep until ((newlike GT like) OR $
              (randomu(seed) LT (newlike/(newlike+like))))
return
end