;;; -*-  Mode: Lisp -*- 
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;;;                                                                              
;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>		 
;;;  		       								 
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;;
;; Critical pair queue implementation
;;
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(defpackage "PAIR-QUEUE"
  (:use :cl :priority-queue :monom :polynomial :utils)
  (:export "SUGAR-PAIR-KEY"
	   "PAIR"
	   "MAKE-PAIR"
	   "PAIR-FIRST"
	   "PAIR-SECOND"
	   "PAIR-SUGAR"
	   "PAIR-DIVISION-DATA"
	   "SUGAR-ORDER"
	   "*PAIR-KEY-FUNCTION*"
	   "*PAIR-ORDER*"
	   "MAKE-PAIR-QUEUE"
	   "PAIR-QUEUE-INITIALIZE"
	   "PAIR-QUEUE-INSERT"
	   "PAIR-QUEUE-REMOVE"
	   "PAIR-QUEUE-SIZE"
	   "PAIR-QUEUE-EMPTY-P"
	   "SET-PAIR-HEURISTIC"
	   ))
	   

(in-package :pair-queue)

(defun sugar-pair-key (p q &aux (lcm (universal-lcm (leading-monomial p) (leading-monomial q)))
				(d (sugar lcm)))
  "Returns list (S LCM-TOTAL-DEGREE) where S is the sugar of the S-polynomial of
polynomials P and Q, and LCM-TOTAL-DEGREE is the degree of LCM(LM(P),LM(Q))."
  (declare (type poly p q) (type monom lcm) (type fixnum d))
  (cons (max 
	 (+  (- d (sugar (leading-monomial p))) (poly-sugar p))
	 (+  (- d (sugar (leading-monomial q))) (poly-sugar q)))
	lcm))

(defstruct (pair
	    (:constructor make-pair (first second
					   &aux
					   (sugar (car (sugar-pair-key first second)))
					   (division-data nil))))
  (first nil :type poly)
  (second nil :type poly)
  (sugar 0 :type fixnum)
  (division-data nil :type list))
  
;;(defun pair-sugar (pair &aux (p (pair-first pair)) (q (pair-second pair)))
;;  (car (sugar-pair-key p q)))

(defun sugar-order (x y)
  "Pair order based on sugar, ties broken by normal strategy."
  (declare (type cons x y))
  (or (< (car x) (car y))
      (and (= (car x) (car y))
	   (< (total-degree (cdr x))
	      (total-degree (cdr y))))))

(defvar *pair-key-function* #'sugar-pair-key
  "Function that, given two polynomials as argument, computed the key
in the pair queue.")

(defvar *pair-order* #'sugar-order
  "Function that orders the keys of pairs.")

(defun make-pair-queue ()
  "Constructs a priority queue for critical pairs."
  (make-priority-queue
   :element-type 'pair
   :element-key #'(lambda (pair) (funcall *pair-key-function* (pair-first pair) (pair-second pair)))
   :test *pair-order*))

(defun pair-queue-initialize (pq f start
			      &aux
			      (s (1- (length f)))
			      (b (nconc (makelist (make-pair (elt f i) (elt f j))
						 (i 0 (1- start)) (j start s))
					(makelist (make-pair (elt f i) (elt f j))
						 (i start (1- s)) (j (1+ i) s)))))
  "Initializes the priority for critical pairs. F is the initial list of polynomials.
START is the first position beyond the elements which form a partial
grobner basis, i.e. satisfy the Buchberger criterion."
  (declare (type priority-queue pq) (type fixnum start))
  (dolist (pair b pq)
    (priority-queue-insert pq pair)))

(defun pair-queue-insert (b pair)
  (priority-queue-insert b pair))

(defun pair-queue-remove (b)
  (priority-queue-remove b))

(defun pair-queue-size (b)
  (priority-queue-size b))

(defun pair-queue-empty-p (b)
  (priority-queue-empty-p b))

(defun set-pair-heuristic (method)
  "Sets up variables *PAIR-KEY-FUNCTION* and *PAIR-ORDER* used
to determine the priority of critical pairs in the priority queue."
  (ecase method
    ((sugar :sugar $sugar)
     (setf *pair-key-function* #'sugar-pair-key
	   *pair-order* #'sugar-order))
;     ((minimal-mock-spoly :minimal-mock-spoly $minimal_mock_spoly)
;      (setf *pair-key-function* #'mock-spoly
; 	   *pair-order* #'mock-spoly-order))
    ((minimal-lcm :minimal-lcm $minimal_lcm)
     (setf *pair-key-function* #'(lambda (p q)
				   (universal-lcm (leading-monomial p) (leading-monomial q)))
	   *pair-order* #'reverse-monomial-order))
    ((minimal-total-degree :minimal-total-degree $minimal_total_degree)
     (setf *pair-key-function* #'(lambda (p q)
				   (total-degree
				    (universal-lcm (leading-monomial p) (leading-monomial q))))
	   *pair-order* #'<))
    ((minimal-length :minimal-length $minimal_length)
     (setf *pair-key-function* #'(lambda (p q)
				   (+ (poly-length p) (poly-length q)))
	   *pair-order* #'<))))