;;; -*-  Mode: Lisp -*- 
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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		 
;;;  (at your option) any later version.					 
;;; 		       								 
;;;  This program is distributed in the hope that it will be useful,		 
;;;  but WITHOUT ANY WARRANTY; without even the implied warranty of		 
;;;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the		 
;;;  GNU General Public License for more details.				 
;;; 		       								 
;;;  You should have received a copy of the GNU General Public License		 
;;;  along with this program; if not, write to the Free Software 		 
;;;  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.	 
;;;										 
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;;----------------------------------------------------------------
;; This package implements BASIC OPERATIONS ON MONOMIALS
;;----------------------------------------------------------------
;; DATA STRUCTURES: Conceptually, monomials can be represented as lists:
;;
;; 	monom:	(n1 n2 ... nk) where ni are non-negative integers
;;
;; However, lists may be implemented as other sequence types,
;; so the flexibility to change the representation should be
;; maintained in the code to use general operations on sequences
;; whenever possible. The optimization for the actual representation
;; should be left to declarations and the compiler.
;;----------------------------------------------------------------
;; EXAMPLES: Suppose that variables are x and y. Then
;;
;; 	Monom x*y^2 ---> (1 2)
;;
;;----------------------------------------------------------------

(defpackage "MONOM"
  (:use :cl :ring)
  (:export "MONOM"
	   "EXPONENT"
	   "MAKE-MONOM" 
	   "MAKE-MONOM-VARIABLE" 
	   "MONOM-ELT" 
	   "MONOM-DIMENSION" 
	   "MONOM-TOTAL-DEGREE"
	   "MONOM-SUGAR" 
	   "MONOM-DIV"
	   "MONOM-MUL" 
	   "MONOM-DIVIDES-P"
	   "MONOM-DIVIDES-MONOM-LCM-P"
	   "MONOM-LCM-DIVIDES-MONOM-LCM-P"
	   "MONOM-LCM-EQUAL-MONOM-LCM-P"
	   "MONOM-DIVISIBLE-BY-P"
	   "MONOM-REL-PRIME-P"
	   "MONOM-EQUAL-P"
	   "MONOM-LCM"
	   "MONOM-GCD"
	   "MONOM-DEPENDS-P"
	   "MONOM-MAP"
	   "MONOM-APPEND"
	   "MONOM-CONTRACT"
	   "MONOM->LIST"))

(in-package :monom)

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

(deftype exponent ()
  "Type of exponent in a monomial."
  'fixnum)

(defclass monom ()
  ((dim       :initarg :dim )
   (exponents :initarg :exponents))
  (:default-initargs :dim 0 :exponents nil))

(defmethod print-object ((m monom) stream)
  (princ (slot-value m 'exponents) stream))

;; If a monomial is redefined as structure with slot EXPONENTS, the function
;; below can be the BOA constructor.
(defun make-monom (&key 
		     (dimension nil dimension-suppied-p)
		     (initial-exponents nil initial-exponents-supplied-p)
		     (initial-exponent  nil initial-exponent-supplied-p)
		   &aux
		     (dim (cond (dimension-suppied-p dimension)
				(initial-exponents-supplied-p (length initial-exponents))
				(t (error "You must provide DIMENSION or INITIAL-EXPONENTS"))))
		     (exponents (cond 
				  ;; when exponents are supplied
				  (initial-exponents-supplied-p
				   (make-array (list dim) :initial-contents initial-exponents
					       :element-type 'exponent))
				  ;; when all exponents are to be identical
				  (initial-exponent-supplied-p
				   (make-array (list dim) :initial-element initial-exponent
					       :element-type 'exponent))
				  ;; otherwise, all exponents are zero
				  (t 
				   (make-array (list dim) :element-type 'exponent :initial-element 0)))))
  "A constructor (factory) of monomials. If DIMENSION is given, a sequence of
DIMENSION elements of type EXPONENT is constructed, where individual
elements are the value of INITIAL-EXPONENT, which defaults to 0.
Alternatively, all elements may be specified as a list
INITIAL-EXPONENTS."
  (make-instance 'monom :dim dim :exponents exponents))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Operations on monomials
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(defmethod dimension ((m monom))
  (slot-value m 'dim))

(defmethod ring-elt ((m monom) index)
  "Return the power in the monomial M of variable number INDEX."
  (with-slots (exponents)
      m
    (elt exponents index)))

(defmethod (setf ring-elt) (new-value (m monom) index)
  "Return the power in the monomial M of variable number INDEX."
  (with-slots (exponents)
      m
    (setf (elt exponents index) new-value)))

(defmethod total-degree ((m monom) &optional (start 0) (end (dimension m)))
  "Return the todal degree of a monomoal M. Optinally, a range
of variables may be specified with arguments START and END."
  (declare (type fixnum start end))
  (with-slots (exponents)
      m
    (reduce #'+ exponents :start start :end end)))


(defmethod sugar ((m monom) &aux (start 0) (end (dimension m)))
  "Return the sugar of a monomial M. Optinally, a range
of variables may be specified with arguments START and END."
  (declare (type fixnum start end))
  (with-slots (exponents)
      m
    (total-degree exponents start end)))

(defmethod ring-mul ((m1 monom) (m2 monom))
  "Multiply monomial M1 by monomial M2."
  (with-slots ((exponents1 exponents))
      m1
    (with-slots ((exponents2 exponents))
	m2
      (let* ((exponents (copy-seq exponents1))
	     (dim (reduce #'+ exponents)))
	(map-into exponents #'+ exponents1 exponents2)
	(make-instance 'monom :dim dim :exponents exponents)))))



(defmethod ring-div ((m1 monom) (m2 monom))
  "Divide monomial M1 by monomial M2."
  (with-slots ((exponents1 exponents))
      m1
    (with-slots ((exponents2 exponents))
	m2
      (let* ((exponents (copy-seq exponents1))
	     (dim (reduce #'+ exponents)))
	(map-into exponents #'- exponents1 exponents2)
	(make-instance 'monom :dim dim :exponents exponents)))))

(defmethod divides-p ((m1 monom) (m2 monom))
  "Returns T if monomial M1 divides monomial M2, NIL otherwise."
  (with-slots ((exponents1 exponents))
      m1
    (with-slots ((exponents2 exponents))
	m2
      (every #'<= exponents1 exponents2))))


(defmethod divides-lcm-p ((m1 monom) (m2 monom) (m3 monom))
  "Returns T if monomial M1 divides LCM(M2,M3), NIL otherwise."
  (every #'(lambda (x y z) (<= x (max y z))) 
	 m1 m2 m3))


(defmethod lcm-divides-lcm-p ((m1 monom) (m2 monom) (m3 monom) (m4 monom))
  "Returns T if monomial MONOM-LCM(M1,M2) divides MONOM-LCM(M3,M4), NIL otherwise."
  (declare (type monom m1 m2 m3 m4))
  (every #'(lambda (x y z w) (<= (max x y) (max z w))) 
	 m1 m2 m3 m4))
	 
(defmethod lcm-equal-lcm-p (m1 m2 m3 m4)
  "Returns T if monomial LCM(M1,M2) equals LCM(M3,M4), NIL otherwise."
  (with-slots (exponents1 exponents)
      m1
    (with-slots (exponents2 exponents)
	m2
      (with-slots (exponents3 exponents)
	  m3
	(with-slots (exponents4 exponents)
	    m4
	  (every 
	   #'(lambda (x y z w) (= (max x y) (max z w)))
	   exponents1 exponents2 exponents3 exponents4))))))

(defmethod divisible-by-p ((m1 monom) (m2 monom))
  "Returns T if monomial M1 is divisible by monomial M2, NIL otherwise."

  (every #'>= m1 m2))

(defmethod rel-prime-p ((m1 monom) (m2 monom))
  "Returns T if two monomials M1 and M2 are relatively prime (disjoint)."
  (with-slots (exponents1 exponents)
      m1
    (with-slots (exponents2 exponents)
	m2
      (every #'(lambda (x y) (zerop (min x y))) exponents1 exponents2))))


(defmethod equal-p ((m1 monom) (m2 monom))
  "Returns T if two monomials M1 and M2 are equal."
  (with-slots (exponents1 exponents)
      m1
    (with-slots (exponents2 exponents)
	m2
      (every #'= exponents1 exponents2))))

(defmethod ring-lcm ((m1 monom) (m2 monom)) 
  "Returns least common multiple of monomials M1 and M2."
  (with-slots (exponents1 exponents)
      m1
    (with-slots (exponents2 exponents)
	m2
      (let* ((exponents (copy-seq exponents1))
	     (dim (reduce #'+ exponents)))
	(map-into exponents #'max exponents1 exponents2)
	(make-instance 'monom :dim dim :exponents exponents)))))


(defmethod ring-gcd ((m1 monom) (m2 monom))
  "Returns greatest common divisor of monomials M1 and M2."
  (with-slots (exponents1 exponents)
      m1
    (with-slots (exponents2 exponents)
	m2
      (let* ((exponents (copy-seq exponents1))
	     (dim (reduce #'+ exponents)))
	(map-into exponents #'min exponents1 exponents2)
	(make-instance 'monom :dim dim :exponents exponents)))))

(defmethod depends-p ((m monom) k)
  "Return T if the monomial M depends on variable number K."
  (declare (type fixnum k))
  (with-slots (exponents)
      m
    (plusp (elt exponents k))))

(defmacro monom-map (fun m &rest ml &aux (result `(copy-seq ,m)))
  "Map function FUN of one argument over the powers of a monomial M.
Fun should map a single FIXNUM argument to FIXNUM.  Return a sequence
of results."
  `(map-into ,result ,fun ,m ,@ml))

(defun monom-append (m1 m2 &aux (dim (+ (length m1) (length m2))))
  (declare (type monom m1 m2) (fixnum dim))
  (concatenate `(monom ,dim) m1 m2))

(defun monom-contract (m k)
  "Drop the first K variables in monomial M."
  (declare (type monom m) (fixnum k))
  (subseq m k))

(defun make-monom-variable (nvars pos &optional (power 1)
			    &aux (m (make-monom :dimension nvars)))
  "Construct a monomial in the polynomial ring
RING[X[0],X[1],X[2],...X[NVARS-1]] over the (unspecified) 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. "
  (declare (type fixnum nvars pos power) (type monom m))
  (setf (monom-elt m pos) power)
  m)

(defun monom->list (m)
  "A human-readable representation of a monomial M as a list of exponents."  
  (declare (type monom m))
  (coerce m 'list))
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