;;; -*-  Mode: Lisp -*- 
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;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>		 
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(defpackage "PAIR-QUEUE"
  (:use :cl :priority-queue :monom :polynomial :utils)
  (:export "CRITICAL-PAIR"
	   "CRITICAL-PAIR-FIRST"
	   "CRITICAL-PAIR-SECOND"
	   "MAKE-PAIR-QUEUE"
	   "PAIR-QUEUE-INITIALIZE"
	   "PAIR-QUEUE-INSERT"
	   "PAIR-QUEUE-REMOVE"
	   "PAIR-QUEUE-SIZE"
	   "PAIR-QUEUE-EMPTY-P"
	   "SET-PAIR-HEURISTIC"
	   )
  (:documentation "Critical pair queue implementation. The pair queue is a list of critical
pairs, ordered by some partial order. Pair queue is a kind of priority queue.")
  )
	   
(in-package :pair-queue)

(defclass critical-pair ()
  ((first :initform nil  :initarg :first :accessor critical-pair-first :type poly)
   (second :initform nil :initarg :second :accessor critical-pair-second :type poly))
  (:documentation "Represents a critical pair, i.e. a pair of two polynomials. The derived
classes may add extra data used in computing the order of critical pairs."))

(defmethod print-object ((self critical-pair) stream)
  (print-unreadable-object (self stream :type t :identity t)
    (with-accessors ((first critical-pair-first)
		     (second critical-pair-second))
	self
      (format stream "FIRST=~A SECOND=~A" 
	      first second))))

(defclass selection-strategy ()
  ((pair-key-fn   :initform (error "Must specify PAIR-KEY-FN") :initarg :pair-key-fn :accessor pair-key-fn)
   (pair-order-fn :initform (error "Must specify PAIR-ORDER-FN") :initarg :pair-order-fn :accessor pair-order-fn))
  (:documentation "Represents a critical pair selection strategy.  The
two ingredients of a strategy is a function PAIR-KEY-FUNCTION which
computes a key from the critical pair, which can be any type of data,
and a function PAIR-ORDER-FN used to compaire the calculated keys to
determine which pair is more promising and should be considered first."))

(defmethod print-object ((self selection-strategy) stream)
  (print-unreadable-object (self stream :type t :identity t)
    (with-accessors ((pair-key-fn pair-key-fn)
		     (pair-order-fn pair-order-fn))
	self
      (format stream "PAIR-KEY-FN=~A PAIR-ORDER-FN=~A" 
	      pair-key-fn pair-order-fn))))

(defclass normal-selection-strategy (selection-strategy) 
  ((pair-key-fn :initform #'(lambda (p q) (universal-lcm (leading-monomial p) (leading-monomial q))))
   (pair-order-fn :initform #'lex>))
  (:documentation "The normal selection strategy for a given monomial order MONOMIAL-ORDER-FN. A pair
with the minimal LCM of leading monomials is selected."))

(defclass min-total-degree-strategy (selection-strategy)
  ((pair-key-fn :initform #'(lambda (p q) (total-degree (universal-lcm (leading-monomial p) (leading-monomial q)))))
   (pair-order :initform #'<))
  (:documentation "Make a selection strategy where a pair with a
minimum total degree of LCM of leading monomials is selected."))

(defclass minimal-length-strategy (selection-strategy)
  ((pair-key-fn :initform #'(lambda (p q) (+ (poly-length p) (poly-length q))))
   (pair-order :initform #'<))
  (:documentation "Make a selection strategy where a pair with the minimum combined length of both
polynomials is selected."))

(defclass critical-pair-queue (selection-strategy)
  ((pq :type priority-queue)))

(defmethod initialize-instance :after ((self critical-pair-queue) &key)
  (make-priority-queue
   :element-type 'critical-pair
   :element-key #'(lambda (pair) (funcall pair-key-fn (critical-pair-first pair) (critical-pair-second pair)))
   :test pair-order-fn))

(defun pair-queue-initialize (pq f start
			      &aux
			      (s (1- (length f)))
			      (b (nconc (makelist (make-instance 'critical-pair :first (elt f i) :second (elt f j))
						 (i 0 (1- start)) (j start s))
					(makelist (make-instance 'critical-pair :first (elt f i) :second (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))