source: branches/f4grobner/pair-queue.lisp@ 3946

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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 #'(lambda (p q) (universal-lcm (leading-monomial p) (leading-monomial q))) :initarg :pair-key-fn :accessor pair-key-fn)
   (pair-order-fn :initform #'lex> :initarg :pair-order-fn :accessor pair-order-fn))
  (:documentation "Represents the normal 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.  The normal selection strategy for a given
monomial order PAIR-ORDER-FN consists in selecting the pair with the
minimal LCM of leading monomials 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 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-fn :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-fn :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 :initform nil :initarg :pq :accessor pq :type priority-queue)))

(defmethod initialize-instance :after ((self critical-pair-queue) &key (f nil) (start 1))
  (with-accessors ((pair-key-fn pair-key-fn)
                   (pair-order-fn pair-order-fn)
                   (pq pq))
      self
    (setf pq (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))
    (let* ((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)))))
      (dolist (pair b pq)
        (priority-queue-insert pq pair)))
    ))

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


(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))