source: branches/f4grobner/term.lisp@ 797

;;; -*-  Mode: Lisp; Package: Maxima; Syntax: Common-Lisp; Base: 10 -*- 
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;;;                                                                              
;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>          
;;;                                                                              
;;;  This program is free software; you can redistribute it and/or modify        
;;;  it under the terms of the GNU General Public License as published by        
;;;  the Free Software Foundation; either version 2 of the License, or           
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;;;  but WITHOUT ANY WARRANTY; without even the implied warranty of              
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;;;  GNU General Public License for more details.                                
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;;;  You should have received a copy of the GNU General Public License           
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(defpackage "TERM"
  (:use :cl :monomial :ring)
  (:export "TERM"
           "TERM-EXPONENTS"
           "TERM-COEFF"
           "MAKE-TERM"
           "MAKE-TERM-VARIABLE"
           "TERM-MUL"
           "TERM-SUGAR"))


(in-package :term)

(defstruct (term
             (:include monom)
             ;; BOA constructor. TODO: avoid code duplication with MONOM?
             (:constructor make-term (monom &key (coeff nil coeff-supplied-p)
                                            (ring *ring-of-integers* ring-supplied-p)
                                            &aux
                                            (coeff (cond 
                                                     (coeff-supplied-p coeff)
                                                     (ring-supplied-p (funcall (ring-unit ring)))
                                                     (t 
                                                      (error "Coefficient or ring must be supplied."))))
                                            (exponents (monom-exponents monom))))
             ;;(:constructor make-term-variable)
             ;;(:type list)
             )
  (coeff nil))


(defun make-term-variable (ring nvars pos
                                &optional
                                (power 1)
                                (coeff (funcall (ring-unit ring))))
  "Construct a term in the polynomial ring RING[X[0],X[1],X[2],...X[NVARS-1]]
over the ring RING which represents a single variable. It assumes
number of variables NVARS and the variable is at position
POS. Optionally, the variable may appear raised to power POWER.
Optionally, the term may appear with an arbitrary coefficient, which
defaults to the unit of the RING."
  (declare (fixnum nvars pos power))
  (let ((result (make-term (make-monom nvars) :coeff coeff)))
    (setf (monom-elt result pos) power)
    result))

(defun term-mul (ring term1 term2)
  "Returns the product of the terms TERM1 and TERM2,
or NIL when the product is 0. This definition takes care of divisors of 0
in the coefficient ring."
  (let ((c (funcall (ring-mul ring) (term-coeff term1) (term-coeff term2))))
    (unless (funcall (ring-zerop ring) c)
      (make-term (monom-mul term1 term2) c))))

(defun term-sugar (term)
  (monom-sugar term))