source: branches/f4grobner/term.lisp@ 3436

;;; -*-  Mode: Lisp -*- 
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;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>          
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;;;  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        
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;;;  GNU General Public License for more details.                                
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(defpackage "TERM"
  (:use :cl :monom :ring)
  (:export "TERM")
  (:documentation "This package implements class TERM. A term is a
product of a scalar and powers of some variables, such as
5*X^2*Y^3. The part of the term without the coefficient is a monomial
X^2*Y^3, which is represented by class MONOM, provided by the :MONOM
package. In this implementation, a TERM specializes MONOL. Also, a
monomial can be considered a TERM whose coefficient is the unit
element (1) of the underlying ring. The generic method CHANGE-CLASS
can be used to convert between a MONOM and a TERM, observing this
convention."))

(in-package :term)

(proclaim '(optimize (speed 3) (space 0) (safety 0) (debug 0)))

;; NOTE: Since term does not have slots of its own,
;; INITIALIZE-INSTANCE is not called by MAKE-INSTANCE.
(defclass term (monom scalar)
  ()
  (:documentation "Implements a term, i.e. a product of a scalar
and powers of some variables, such as 5*X^2*Y^3."))

(defmethod print-object ((self term) stream)
  (print-unreadable-object (self stream :type t :identity t)
    (with-accessors ((exponents monom-exponents)
                     (coeff scalar-coeff))
        self
      (format stream "EXPONENTS=~A COEFF=~A"
              exponents coeff))))


(defmethod r-equalp ((term1 term) (term2 term))
  (when (r-equalp (scalar-coeff term1) (scalar-coeff term2))
    (call-next-method)))

(defmethod update-instance-for-different-class :after ((old monom) (new  scalar) &key)
  (setf (scalar-coeff new) 1))

(defmethod multiply-by :before ((self term) (other term))
  "Destructively multiply terms SELF and OTHER and store the result into SELF.
It returns SELF."
  (setf (scalar-coeff self) (multiply-by (scalar-coeff self) (scalar-coeff other))))

(defmethod left-tensor-product-by ((self term) (other term))
  (setf (scalar-coeff self) (multiply-by (scalar-coeff self) (scalar-coeff other)))
  (call-next-method))

(defmethod right-tensor-product-by ((self term) (other term))
  (setf (scalar-coeff self) (multiply-by (scalar-coeff self) (scalar-coeff other)))
  (call-next-method))

(defmethod left-tensor-product-by ((self term) (other monom))
  (call-next-method))

(defmethod right-tensor-product-by ((self term) (other monom))
  (call-next-method))

(defmethod divide-by ((self term) (other term))
  "Destructively divide term SELF by OTHER and store the result into SELF.
It returns SELF."
  (setf (scalar-coeff self) (divide-by (scalar-coeff self) (scalar-coeff other)))
  (call-next-method))

(defmethod unary-minus ((self term))
  (setf (scalar-coeff self) (unary-minus (scalar-coeff self)))
  self)

(defmethod r* ((term1 term) (term2 term))
  "Non-destructively multiply TERM1 by TERM2."
  (multiply-by (copy-instance term1) (copy-instance term2)))

(defmethod r* ((term1 number) (term2 monom))
  "Non-destructively multiply TERM1 by TERM2."
  (r* term1 (change-class (copy-instance term2) 'term)))

(defmethod r* ((term1 number) (term2 term))
  "Non-destructively multiply TERM1 by TERM2."
  (setf (scalar-coeff term2) 
        (r* term1 (scalar-coeff term2)))
  term2)

(defmethod r-zerop ((self term))
  (r-zerop (scalar-coeff self)))

#|

(defun term->cons (term) 
  "A human-readable representation of a term as a cons (MONOM . COEFF)."
  (declare (type term term))
  (cons (monom->list (term-monom term)) (scalar-coeff term)))

|#