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source: branches/f4grobner/term.lisp@ 2761

Last change on this file since 2761 was 2730, 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" "MAKE-TERM-VARIABLE")
25 (:documentation "This package implements class TERM. A term is a
26product of a scalar and powers of some variables, such as
275*X^2*Y^3. The part of the term without the coefficient is a monomial
28X^2*Y^3, which is represented by class MONOM, provided by the :MONOM
29package. In this implementation, a TERM specializes MONOL. Also, a
30monomial can be considered a TERM whose coefficient is the unit
31element (1) of the underlying ring. The generic method CHANGE-CLASS
32can be used to convert between a MONOM and a TERM, observing this
33convention."))
34
35(in-package :term)
36
37(proclaim '(optimize (speed 3) (space 0) (safety 0) (debug 0)))
38
39(defclass term (monom)
40 ((coeff :initarg :coeff :accessor term-coeff
41 :documentation "The coefficient."))
42 (:default-initargs :dimension nil :exponents nil :coeff nil)
43 (:documentation "Implements a term, i.e. a product of a ring element
44and powers of some variables, such as 5*X^2*Y^3."))
45
46(defmethod r-coeff ((self term))
47 (term-coeff self))
48
49(defmethod (setf r-coeff) (new-value (self term))
50 (setf (term-coeff self) new-value))
51
52(defun term-equalp (term1 term2)
53 (declare (type term term1 term2))
54 (and (monom-equalp term1 term2)
55 (r-equalp (term-coeff term1) (term-coeff term2))))
56
57(defmethod r-equalp ((term1 term) (term2 term))
58 (term-equalp term1 term2))
59
60(defmethod print-object ((self term) stream)
61 (format stream "#<TERM DIMENSION=~A EXPONENTS=~A COEFF=~A>"
62 (r-dimension self)
63 (r-exponents self)
64 (r-coeff self)))
65
66(defmethod shared-initialize ((self term) slot-names
67 &rest
68 initargs
69 &key
70 coeff
71 &allow-other-keys)
72 (declare (ignore initargs))
73 (if (eq slot-names t) (setf slot-names '(coeff)))
74 (dolist (slot-name slot-names)
75 (case slot-name
76 (coeff
77 (setf (slot-value self 'coeff) coeff)))))
78
79(defmethod update-instance-for-different-class :after ((old monom)
80 (new term)
81 &key)
82 ;; Changing an instance of class MONOM to class TERM may also
83 ;; happen when OLD is an instance of TERM, in which case the
84 ;; value of the coefficient should be preserved.
85 ;; This implementation calls R-COEFF, which satisfies
86 ;; this requirement.
87 (setf (slot-value new 'coeff) (r-coeff old)))
88
89
90#|
91(defun make-term-variable (nvars pos
92 &optional
93 (power 1)
94 (coeff 1))
95 "Construct a term in the polynomial ring RING[X[0],X[1],X[2],...X[NVARS-1]]
96over the ring RING which represents a single variable. It assumes
97number of variables NVARS and the variable is at position
98POS. Optionally, the variable may appear raised to power POWER.
99Optionally, the term may appear with an arbitrary coefficient, which
100defaults to the unit of the RING."
101 (declare (type fixnum nvars pos))
102 (make-term :monom (make-monom-variable nvars pos power)
103 :coeff coeff))
104
105|#
106
107(defmethod r* :around ((term1 term) (term2 term))
108 "Returns the product of the terms TERM1 and TERM2,
109or NIL when the product is 0. This definition takes care of divisors of 0
110in the coefficient ring."
111 (let ((result (change-class (call-next-method) 'term)))
112 (setf (r-coeff result) (r* (r-coeff term1) (r-coeff term2)))
113 result))
114
115(defmethod multiply-by ((self term) (other monom))
116 "Returns the product of the terms TERM1 and TERM2,
117or NIL when the product is 0. This definition takes care of divisors of 0
118in the coefficient ring."
119 (setf (r-coeff self) (multiply-by (r-coeff self) (r-coeff other)))
120 self)
121
122(defmethod multiply-by ((self term) (other scalar))
123 "Returns the product of the terms TERM1 and TERM2,
124or NIL when the product is 0. This definition takes care of divisors of 0
125in the coefficient ring."
126 (setf (r-coeff self) (multiply-by (r-coeff self) other))
127 self)
128
129(defmethod unary-minus ((self term))
130 (setf (term-coeff self) (unary-minus (term-coeff self)))
131 self)
132
133#|
134
135(defun term->cons (term)
136 "A human-readable representation of a term as a cons (MONOM . COEFF)."
137 (declare (type term term))
138 (cons (monom->list (term-monom term)) (term-coeff term)))
139
140|#
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