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source: branches/f4grobner/term.lisp@ 2973

Last change on this file since 2973 was 2973, checked in by Marek Rychlik, 9 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 "TERM"
23 (:use :cl :monom :ring)
24 (:export "TERM"
25 "MAKE-TERM-VARIABLE"
26 )
27 (:documentation "This package implements class TERM. A term is a
28product of a scalar and powers of some variables, such as
295*X^2*Y^3. The part of the term without the coefficient is a monomial
30X^2*Y^3, which is represented by class MONOM, provided by the :MONOM
31package. In this implementation, a TERM specializes MONOL. Also, a
32monomial can be considered a TERM whose coefficient is the unit
33element (1) of the underlying ring. The generic method CHANGE-CLASS
34can be used to convert between a MONOM and a TERM, observing this
35convention."))
36
37(in-package :term)
38
39(proclaim '(optimize (speed 3) (space 0) (safety 0) (debug 0)))
40
41(defclass term (monom)
42 ((coeff :initarg :coeff :accessor term-coeff
43 :documentation "The coefficient."))
44 (:default-initargs :dimension nil :exponents nil :coeff nil)
45 (:documentation "Implements a term, i.e. a product of a ring element
46and powers of some variables, such as 5*X^2*Y^3."))
47
48(defmethod r-coeff ((self term))
49 (term-coeff self))
50
51(defmethod (setf r-coeff) (new-value (self term))
52 (setf (term-coeff self) new-value))
53
54(defmethod r-equalp ((term1 term) (term2 term))
55 (and (r-equalp (term-coeff term1) (term-coeff term2))
56 (call-next-method)))
57
58(defmethod print-object ((self term) stream)
59 (format stream "#<TERM DIMENSION=~A EXPONENTS=~A COEFF=~A>"
60 (r-dimension self)
61 (r-exponents self)
62 (r-coeff self)))
63
64(defmethod shared-initialize ((self term) slot-names
65 &rest
66 initargs
67 &key
68 coeff
69 &allow-other-keys)
70 (declare (ignore initargs))
71 (if (eq slot-names t) (setf slot-names '(coeff)))
72 (dolist (slot-name slot-names)
73 (case slot-name
74 (coeff
75 (setf (slot-value self 'coeff) coeff)))))
76
77(defmethod update-instance-for-different-class :after ((old monom) (new term) &key)
78 ;; Changing an instance of class MONOM to class TERM may also
79 ;; happen when OLD is an instance of TERM, in which case the
80 ;; value of the coefficient should be preserved.
81 (unless (slot-boundp new 'coeff)
82 (setf (term-coeff new) 1))
83 self)
84
85#|
86(defun make-term-variable (nvars pos
87 &optional
88 (power 1)
89 (coeff 1))
90 "Construct a term in the polynomial ring RING[X[0],X[1],X[2],...X[NVARS-1]]
91over the ring RING which represents a single variable. It assumes
92number of variables NVARS and the variable is at position
93POS. Optionally, the variable may appear raised to power POWER.
94Optionally, the term may appear with an arbitrary coefficient, which
95defaults to the unit of the RING."
96 (declare (type fixnum nvars pos))
97 (make-term :monom (make-monom-variable nvars pos power)
98 :coeff coeff))
99
100|#
101
102(defmethod multiply-by :before ((self term) (other term))
103 "Destructively multiply terms SELF and OTHER and store the result into SELF.
104It returns SELF."
105 (setf (r-coeff self) (multiply-by (r-coeff self) (r-coeff other))))
106
107(defmethod divide-by ((self term) (other term))
108 "Destructively divide term SELF by OTHER and store the result into SELF.
109It returns SELF."
110 (setf (r-coeff self) (divide-by (r-coeff self) (r-coeff other)))
111 (call-next-method))
112
113(defmethod unary-minus ((self term))
114 (setf (term-coeff self) (unary-minus (term-coeff self)))
115 self)
116
117(defmethod r* ((term1 term) (term2 term))
118 "Non-destructively multiply TERM1 by TERM2."
119 (multiply-by (copy-instance term1) (copy-instance term2)))
120
121(defmethod r-zerop ((self term))
122 (r-zerop (term-coeff self)))
123
124#|
125
126(defun term->cons (term)
127 "A human-readable representation of a term as a cons (MONOM . COEFF)."
128 (declare (type term term))
129 (cons (monom->list (term-monom term)) (term-coeff term)))
130
131|#
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