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source: branches/f4grobner/term.lisp@ 1921

Last change on this file since 1921 was 1903, 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 "TERM-EXPONENTS"
26 "TERM-MONOM"
27 "TERM-COEFF"
28 "MAKE-TERM"
29 "MAKE-TERM-VARIABLE"
30 "TERM-MUL"
31 "TERM-SUGAR"
32 "TERM-DEPENDS-P"
33 "TERM->CONS"))
34
35
36(in-package :term)
37
38(defstruct (term
39 ;; A simple BOA constructor
40 ;;(:constructor make-term (monom coeff))
41 ;;(:constructor make-term-variable)
42 ;;(:type list)
43 )
44 (monom nil :type monom)
45 (coeff nil))
46
47
48(defun make-term-variable (ring nvars pos
49 &optional
50 (power 1)
51 (coeff (funcall (ring-unit ring))))
52 "Construct a term in the polynomial ring RING[X[0],X[1],X[2],...X[NVARS-1]]
53over the ring RING which represents a single variable. It assumes
54number of variables NVARS and the variable is at position
55POS. Optionally, the variable may appear raised to power POWER.
56Optionally, the term may appear with an arbitrary coefficient, which
57defaults to the unit of the RING."
58 (declare (type ring ring) (type fixnum nvars pos))
59 (make-term :monom (make-monom-variable nvars pos power) :coeff coeff))
60
61(defun term-mul (ring term1 term2)
62 "Returns the product of the terms TERM1 and TERM2,
63or NIL when the product is 0. This definition takes care of divisors of 0
64in the coefficient ring."
65 (declare (type ring ring) (type term term1 term2))
66 (let ((c (funcall (ring-mul ring) (term-coeff term1) (term-coeff term2))))
67 (unless (funcall (ring-zerop ring) c)
68 (make-term :monom (monom-mul (term-monom term1) (term-monom term2)) :coeff c))))
69
70(defun term-sugar (term)
71 (declare (type term term))
72 (monom-sugar (term-monom term)))
73
74;; Does the term depend on variable K?
75(defun term-depends-p (term k)
76 "Return T if the term TERM depends on variable number K."
77 (declare (type term term) (type fixnum k))
78 (monom-depends-p (term-monom term) k))
79
80(defun term->cons (term)
81 "A human-readable representation of a term as a cons (MONOM . COEFF)."
82 (declare (type term term))
83 (cons (monom->list (term-monom term)) (term-coeff term)))
84
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