;;;; Created on 2007-03-21 17:56:00

(defun metropolis (&key (steps 10000)
                        (cost 'cost)
                        (next 'mutate)
                        (first 'start)
                        (near  0.001)) 
  (let* (best
          (time 1) 
          (bestS (expt 10 32))
          new
          newS
          (current (funcall first))
          (currentS (funcall cost current)))
    (loop
      (if (<= time 0 ) 
          (return (values best bestS)))
      (setf new  (funcall next current)
            newS (funcall cost new)) 
      (if (< newS bestS)
          (progn  ;(format t " !~a old ~a new ~a delta ~a~%" (say time) (say bestS) (say newS) (say (- bestS newS)))
                  (format t " !~a ~a~%"  (say time) (say (- bestS newS)))
                 (setf best   (copy-list new)
                       bestS  newS)))
      (if (accept (- newS currentS) time)
          (setf current  (copy-list new)
                currentS newS))
      (setf time 
            (- time (/ 1.0 steps)))
      )))

(defun accept(delta time)
  (cond ((< delta 0)
         ;(format t "-~a" (say time))
         t)
        ((< (random 1.0)
            (expt 2.781281828
                  (* -1.0 (/ delta time))))
         ;(format t "+~a" (say time))
         t)
        (t nil)))