;;; -*-  Mode: Lisp -*- 
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;;;                                                                              
;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>		 
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(defpackage "MONOM"
  (:use :cl :ring)
  (:export "MONOM"
	   "EXPONENT"
	   "MAKE-MONOM-VARIABLE")
  (:documentation
   "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) "))

(in-package :monom)

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

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

(defclass monom ()
  ((dimension          :initarg :dimension :accessor r-dimension)
   (exponents :initarg :exponents :accessor r-exponents))
  (:default-initargs :dimension nil :exponents nil :exponent nil))

(defmethod print-object ((self monom) stream)
  (format stream "#<MONOM DIMENSION=~A EXPONENTS=~A>"
	  (r-dimension self)
	  (r-exponents self)))

(defmethod shared-initialize :after ((self monom) slot-names
				     &key 
				       dimension
				       exponents
				       exponent
				     &allow-other-keys
				       )
  (if (eq slot-names t) (setf slot-names '(dimension exponents)))
  (dolist (slot-name slot-names)
    (case slot-name
      (dimension 
       (cond (dimension 
	      (setf (slot-value self 'dimension) dimension))
	     (exponents
	      (setf (slot-value self 'dimension) (length exponents)))
	     (t 
	      (error "DIMENSION or EXPONENTS must not be NIL"))))
      (exponents  
       (cond 
	 ;; when exponents are supplied
	 (exponents
	  (let ((dim (length exponents)))
	    (when (and dimension (/= dimension dim))
	      (error "EXPONENTS must have length DIMENSION")) 
	    (setf (slot-value self 'dimension) dim
		  (slot-value self 'exponents) (make-array dim :initial-contents exponents))))
	 ;; when all exponents are to be identical
	 (t
	  (let ((dim (slot-value self 'dimension)))
	    (setf (slot-value self 'exponents)
		  (make-array (list dim) :initial-element (or exponent 0)
			      :element-type 'exponent)))))))))

(defgeneric monom= (object1 object2)
  (:method ((object1 monom) (object2 monom))
    (equal (r-exponents object1) (r-exponents object2))))

(defmethod r-coeff ((m monom))
  "A MONOM can be treated as a special case of TERM,
where the coefficient is 1."
  1)
  
(defmethod r-elt ((m monom) index)
  "Return the power in the monomial M of variable number INDEX."
  (with-slots (exponents)
      m
    (elt exponents index)))

(defmethod (setf r-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 r-total-degree ((m monom) &optional (start 0) (end (r-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 r-sugar ((m monom) &aux (start 0) (end (r-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))
    (r-total-degree m start end))

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

(defmethod multiply-by ((self monom) (other monom))
  (with-slots ((exponents1 exponents))
      self
    (with-slots ((exponents2 exponents))
	other
      (map-into exponents1 #'+ exponents1 exponents2)))
  self)

(defmethod r/ ((m1 monom) (m2 monom))
  "Divide monomial M1 by monomial M2."
  (with-slots ((exponents1 exponents) (dimension1 dimension))
      m1
    (with-slots ((exponents2 exponents))
	m2
      (let* ((exponents (copy-seq exponents1))
	     (dimension dimension1))
	(map-into exponents #'- exponents1 exponents2)
	(make-instance 'monom :dimension dimension :exponents exponents)))))

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

(defmethod r-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 r-equalp ((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 r-lcm ((m1 monom) (m2 monom)) 
  "Returns least common multiple of monomials M1 and M2."
  (with-slots ((exponents1 exponents) (dimension1 dimension))
      m1
    (with-slots ((exponents2 exponents))
	m2
      (let* ((exponents (copy-seq exponents1))
	     (dimension dimension1))
	(map-into exponents #'max exponents1 exponents2)
	(make-instance 'monom :dimension dimension :exponents exponents)))))


(defmethod r-gcd ((m1 monom) (m2 monom))
  "Returns greatest common divisor of monomials M1 and M2."
  (with-slots ((exponents1 exponents) (dimension1 dimension))
      m1
    (with-slots ((exponents2 exponents))
	m2
      (let* ((exponents (copy-seq exponents1))
	     (dimension dimension1))
	(map-into exponents #'min exponents1 exponents2)
	(make-instance 'monom :dimension dimension :exponents exponents)))))

(defmethod r-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))))

(defmethod r-tensor-product ((m1 monom) (m2 monom))
  (with-slots ((exponents1 exponents) (dimension1 dimension))
      m1
    (with-slots ((exponents2 exponents) (dimension2 dimension))
	m2
      (make-instance 'monom 
		     :dimension (+ dimension1 dimension2)
		     :exponents (concatenate 'vector exponents1 exponents2)))))

(defmethod r-contract ((m monom) k)
  "Drop the first K variables in monomial M."
  (declare (fixnum k))
  (with-slots (dimension exponents) 
      m
    (setf dimension (- dimension k)
	  exponents (subseq exponents k))))

(defun make-monom-variable (nvars pos &optional (power 1)
			    &aux (m (make-instance '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))
  (with-slots (exponents)
      m
    (setf (elt exponents pos) power)
    m))

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