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source: branches/f4grobner/pair-queue.lisp@ 4186

Last change on this file since 4186 was 4186, checked in by Marek Rychlik, 8 years ago

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1;;; -*- Mode: Lisp -*-
2;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
3;;;
4;;; Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>
5;;;
6;;; This program is free software; you can redistribute it and/or modify
7;;; it under the terms of the GNU General Public License as published by
8;;; the Free Software Foundation; either version 2 of the License, or
9;;; (at your option) any later version.
10;;;
11;;; This program is distributed in the hope that it will be useful,
12;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
13;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14;;; GNU General Public License for more details.
15;;;
16;;; You should have received a copy of the GNU General Public License
17;;; along with this program; if not, write to the Free Software
18;;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19;;;
20;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
21
22(defpackage "PAIR-QUEUE"
23 (:use :cl :priority-queue :monom :polynomial :symbolic-polynomial :utils)
24 (:export "CRITICAL-PAIR"
25 "CRITICAL-PAIR-FIRST"
26 "CRITICAL-PAIR-SECOND"
27 "CRITICAL-PAIR-QUEUE"
28 "SELECTION-STRATEGY"
29 "+NORMAL-STRATEGY+"
30 "+MIN-TOTAL-DEGREE-STRATEGY+"
31 "+MIN-COMBINED-LENGTH-STRATEGY+"
32 "MAKE-CRITICAL-PAIR-QUEUE"
33 "MAKE-CRITICAL-PAIRS"
34 )
35 (:documentation "Critical pair queue implementation. The pair queue is a list of critical
36pairs, ordered by some partial order. Pair queue is a kind of priority queue.")
37 )
38
39(in-package :pair-queue)
40
41(defclass critical-pair ()
42 ((first :initform nil :initarg :first :accessor critical-pair-first :type poly)
43 (second :initform nil :initarg :second :accessor critical-pair-second :type poly))
44 (:documentation "Represents a critical pair, i.e. a pair of two polynomials. The derived
45classes may add extra data used in computing the order of critical pairs."))
46
47(defmethod print-object ((self critical-pair) stream)
48 (print-unreadable-object (self stream :type t :identity t)
49 (with-accessors ((first critical-pair-first)
50 (second critical-pair-second))
51 self
52 (format stream "FIRST=~A SECOND=~A"
53 first second))))
54
55(defclass selection-strategy ()
56 ((pair-key-fn :initform (error "Initarg :pair-key-fn must be specified.")
57 :initarg :pair-key-fn
58 :accessor pair-key-fn)
59 (pair-order-fn :initform (error "Initarg :pair-order-fn must be specified.")
60 :initarg :pair-order-fn
61 :accessor pair-order-fn))
62 (:documentation "The two ingredients of a strategy is a function
63PAIR-KEY-FUNCTION which computes a key from the critical pair, which
64can be any type of data, and a function PAIR-ORDER-FN used to compaire
65the calculated keys to determine which pair is more promising and
66should be considered first. The normal selection strategy for a given
67monomial order PAIR-ORDER-FN consists in selecting the pair with the
68minimal LCM of leading monomials first."))
69
70(defmethod print-object ((self selection-strategy) stream)
71 (print-unreadable-object (self stream :type t :identity t)
72 (with-accessors ((pair-key-fn pair-key-fn)
73 (pair-order-fn pair-order-fn))
74 self
75 (format stream "PAIR-KEY-FN=~A PAIR-ORDER-FN=~A"
76 pair-key-fn pair-order-fn))))
77
78(defparameter +normal-strategy+
79 (make-instance
80 'selection-strategy
81 :pair-key-fn #'(lambda (p q) (universal-lcm (leading-monomial p) (leading-monomial q)))
82 :pair-order-fn #'lex>)
83 "The normal selection strategy where a pair with the largest LCM of
84leading monomials is selected.")
85
86(defparameter +min-total-degree-strategy+
87 (make-instance
88 'selection-strategy
89 :pair-key-fn #'(lambda (p q) (total-degree (universal-lcm (leading-monomial p) (leading-monomial q))))
90 :pair-order-fn #'<)
91 "A selection strategy where a pair with a minimum total degree of
92 LCM of leading monomials is selected.")
93
94(defparameter +min-combined-length-strategy+
95 (make-instance
96 'selection-strategy
97 :pair-key-fn #'(lambda (p q) (+ (poly-length p) (poly-length q)))
98 :pair-order-fn #'<)
99 "A selection strategy where a pair with the minimum combined length of both
100polynomials is selected.")
101
102(defclass critical-pair-queue (priority-queue)
103 ()
104 (:documentation "Specializes class PRIORITY-QUEUE to ELEMENT-TYPE set to CRITICAL-PAIR."))
105
106(defmethod initialize-instance :before ((self critical-pair-queue) &key)
107 "Initializes the slot ELEMENT-TYPE to symbol CRITICAL-PAIR-QUEUE.
108This overrides the default ELEMENT-TYPE in the superclass."
109 (with-slots ((element-type-x priority-queue::element-type))
110 self
111 (setf element-type-x 'critical-pair))
112 self)
113
114(defun make-critical-pairs (poly-list
115 &optional (start 0)
116 &aux
117 (s (1- (length poly-list))))
118 "Create a list of critical pairs. The argument POLY-LIST is the
119initial list of polynomials and START is the first position beyond the
120elements which form a partial Grobner basis, i.e. satisfy the
121Buchberger criterion."
122 (nconc (makelist (make-instance 'critical-pair :first (elt poly-list i) :second (elt poly-list j))
123 (i 0 (1- start)) (j start s))
124 (makelist (make-instance 'critical-pair :first (elt poly-list i) :second (elt poly-list j))
125 (i start (1- s)) (j (1+ i) s))))
126
127(defgeneric enqueue-critical-pairs (self pair-lst)
128 (:documentation "Place pairs in PAIR-LST on the queue SELF.")
129 (:method ((self critical-pair-queue) pair-lst)
130 "Enqueue into queue QUEUE the elements of the list PAIR-LST."
131 (dolist (pair pair-lst self)
132 (enqueue self pair))))
133
134(defgeneric make-critical-pair-queue (object &optional poly-lst start)
135 (:documentation "Creates a CRITICAL-PAIR-QUEUE from an object OBJECT.")
136 (:method ((object selection-strategy) &optional (poly-lst nil) (start 0))
137 "Creates a CRITICAL-PAIR-QUEUE from a selection strategy OBJECT."
138 (with-slots (pair-key-fn pair-order-fn)
139 object
140 (let ((queue (make-instance 'critical-pair-queue
141 :element-key #'(lambda (pair)
142 (funcall pair-key-fn
143 (critical-pair-first pair)
144 (critical-pair-second pair)))
145 :test pair-order-fn)))
146 (enqueue-critical-pairs queue (make-critical-pairs poly-lst start))))))
147
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