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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 "MONOM"
23 (:use :cl :utils :copy :ring :integer-ring)
24 (:export "MONOM"
25 "TERM"
26 "EXPONENT"
27 "MONOM-DIMENSION"
28 "MONOM-EXPONENTS"
29 "UNIVERSAL-EQUALP"
30 "MONOM-ELT"
31 "TOTAL-DEGREE"
32 "SUGAR"
33 "MULTIPLY-BY"
34 "DIVIDE-BY"
35 "DIVIDE"
36 "MULTIPLY"
37 "DIVIDES-P"
38 "DIVIDES-LCM-P"
39 "LCM-DIVIDES-LCM-P"
40 "LCM-EQUAL-LCM-P"
41 "DIVISIBLE-BY-P"
42 "REL-PRIME-P"
43 "UNIVERSAL-LCM"
44 "UNIVERSAL-GCD"
45 "DEPENDS-P"
46 "LEFT-TENSOR-PRODUCT-BY"
47 "RIGHT-TENSOR-PRODUCT-BY"
48 "LEFT-CONTRACT"
49 "MAKE-MONOM-VARIABLE"
50 "MAKE-MONOM-CONSTANT"
51 "MAKE-TERM-CONSTANT"
52 "->LIST"
53 "->SEXP"
54 "LEX>"
55 "GRLEX>"
56 "REVLEX>"
57 "GREVLEX>"
58 "INVLEX>"
59 "REVERSE-MONOMIAL-ORDER"
60 "MAKE-ELIMINATION-ORDER-FACTORY"
61 "TERM-COEFF"
62 "UNARY-MINUS"
63 "UNARY-INVERSE"
64 "UNIVERSAL-ZEROP")
65 (:documentation
66 "This package implements basic operations on monomials, including
67various monomial orders.
68
69DATA STRUCTURES: Conceptually, monomials can be represented as lists:
70
71 monom: (n1 n2 ... nk) where ni are non-negative integers
72
73However, lists may be implemented as other sequence types, so the
74flexibility to change the representation should be maintained in the
75code to use general operations on sequences whenever possible. The
76optimization for the actual representation should be left to
77declarations and the compiler.
78
79EXAMPLES: Suppose that variables are x and y. Then
80
81 Monom x*y^2 ---> (1 2) "))
82
83(in-package :monom)
84
85(proclaim '(optimize (speed 0) (space 0) (safety 3) (debug 0)))
86
87(deftype exponent ()
88 "Type of exponent in a monomial."
89 'fixnum)
90
91(defclass monom ()
92 ((exponents :initarg :exponents :accessor monom-exponents
93 :documentation "The powers of the variables."))
94 ;; default-initargs are not needed, they are handled by SHARED-INITIALIZE
95 ;;(:default-initargs :dimension 'foo :exponents 'bar :exponent 'baz)
96 (:documentation
97 "Implements a monomial, i.e. a product of powers
98of variables, like X*Y^2."))
99
100(defmethod print-object ((self monom) stream)
101 (print-unreadable-object (self stream :type t :identity t)
102 (with-accessors ((exponents monom-exponents))
103 self
104 (format stream "EXPONENTS=~A"
105 exponents))))
106
107(defmethod initialize-instance :after ((self monom)
108 &key
109 (dimension 0 dimension-supplied-p)
110 (exponents nil exponents-supplied-p)
111 (exponent 0)
112 &allow-other-keys
113 )
114 "The following INITIALIZE-INSTANCE method allows instance initialization
115of a MONOM in a style similar to MAKE-ARRAY, e.g.:
116
117 (MAKE-INSTANCE 'MONOM :EXPONENTS '(1 2 3)) --> #<MONOM EXPONENTS=#(1 2 3)>
118 (MAKE-INSTANCE 'MONOM :DIMENSION 3) --> #<MONOM EXPONENTS=#(0 0 0)>
119 (MAKE-INSTANCE 'MONOM :DIMENSION 3 :EXPONENT 7) --> #<MONOM EXPONENTS=#(7 7 7)>
120
121If both DIMENSION and EXPONENTS are supplied, they must be compatible,
122i.e. the length of EXPONENTS must be equal DIMENSION. If EXPONENTS
123is not supplied, a monom with repeated value EXPONENT is created.
124By default EXPONENT is 0, which results in a constant monomial.
125"
126 (cond
127 (exponents-supplied-p
128 (when (and dimension-supplied-p
129 (/= dimension (length exponents)))
130 (error "EXPONENTS (~A) must have supplied length DIMENSION (~A)"
131 exponents dimension))
132 (let ((dim (length exponents)))
133 (setf (slot-value self 'exponents) (make-array dim :initial-contents exponents))))
134 (dimension-supplied-p
135 ;; when all exponents are to be identical
136 (setf (slot-value self 'exponents) (make-array (list dimension)
137 :initial-element exponent
138 :element-type 'exponent)))
139 (t
140 (error "Initarg DIMENSION or EXPONENTS must be supplied."))))
141
142(defgeneric monom-dimension (self)
143 (:method ((self monom))
144 (length (monom-exponents self))))
145
146(defmethod universal-equalp ((self monom) (other monom))
147 "Returns T iff monomials SELF and OTHER have identical EXPONENTS."
148 (equalp (monom-exponents self) (monom-exponents other)))
149
150(defgeneric monom-elt (m index)
151 (:documentation "Return the power in the monomial M of variable number INDEX.")
152 (:method ((m monom) index)
153 "Return the power in the monomial M of variable number INDEX."
154 (with-slots (exponents)
155 m
156 (elt exponents index))))
157
158(defgeneric (setf monom-elt) (new-value m index)
159 (:documentation "Set the power in the monomial M of variable number INDEX.")
160 (:method (new-value (m monom) index)
161 (with-slots (exponents)
162 m
163 (setf (elt exponents index) new-value))))
164
165(defgeneric total-degree (m &optional start end)
166 (:documentation "Return the total degree of a monomoal M. Optinally, a range
167of variables may be specified with arguments START and END.")
168 (:method ((m monom) &optional (start 0) (end (monom-dimension m)))
169 (declare (type fixnum start end))
170 (with-slots (exponents)
171 m
172 (reduce #'+ exponents :start start :end end))))
173
174(defgeneric sugar (m &optional start end)
175 (:documentation "Return the sugar of a monomial M. Optinally, a range
176of variables may be specified with arguments START and END.")
177 (:method ((m monom) &optional (start 0) (end (monom-dimension m)))
178 (declare (type fixnum start end))
179 (total-degree m start end)))
180
181(defmethod multiply-by ((self monom) (other monom))
182 (with-slots ((exponents1 exponents))
183 self
184 (with-slots ((exponents2 exponents))
185 other
186 (unless (= (length exponents1) (length exponents2))
187 (error "Incompatible dimensions"))
188 (map-into exponents1 #'+ exponents1 exponents2)))
189 self)
190
191(defun multiply (factor &rest more-factors)
192 "Successively multiplies factor FACTOR by the remaining arguments
193MORE-FACTORS, using MULTIPLY-BY to multiply two factors. Thus
194FACTOR may be destructively modified."
195 (reduce #'multiply-by more-factors :initial-value (copy-instance factor)))
196
197(defmethod divide-by ((self monom) (other monom))
198 (with-slots ((exponents1 exponents))
199 self
200 (with-slots ((exponents2 exponents))
201 other
202 (unless (= (length exponents1) (length exponents2))
203 (error "divide-by: Incompatible dimensions."))
204 (unless (every #'>= exponents1 exponents2)
205 (error "divide-by: Negative power would result."))
206 (map-into exponents1 #'- exponents1 exponents2)))
207 self)
208
209(defmethod copy-instance :around ((object monom) &rest initargs &key &allow-other-keys)
210 "An :AROUND method of COPY-INSTANCE. It replaces exponents with a fresh copy of the sequence."
211 (declare (ignore object initargs))
212 (let ((copy (call-next-method)))
213 (setf (monom-exponents copy) (copy-seq (monom-exponents copy)))
214 copy))
215
216(defmethod unary-inverse :before ((self monom))
217 (assert (zerop (total-degree self))
218 nil
219 "Monom ~A must have total degree 0 to be invertible.")
220 self)
221
222(defmethod unary-inverse ((self monom)) self)
223
224(defun divide (numerator &rest denominators)
225 "Successively divides NUMERATOR by elements of DENOMINATORS. The operation
226destructively modifies NUMERATOR."
227 (cond ((endp denominators)
228 (unary-inverse numerator))
229 (t (reduce #'divide-by denominators :initial-value (copy-instance numerator)))))
230
231(defgeneric divides-p (object1 object2)
232 (:documentation "Returns T if OBJECT1 divides OBJECT2.")
233 (:method ((m1 monom) (m2 monom))
234 "Returns T if monomial M1 divides monomial M2, NIL otherwise."
235 (with-slots ((exponents1 exponents))
236 m1
237 (with-slots ((exponents2 exponents))
238 m2
239 (every #'<= exponents1 exponents2)))))
240
241(defgeneric divides-lcm-p (object1 object2 object3)
242 (:documentation "Returns T if OBJECT1 divides LCM(OBJECT2,OBJECT3), NIL otherwise.")
243 (:method ((m1 monom) (m2 monom) (m3 monom))
244 "Returns T if monomial M1 divides LCM(M2,M3), NIL otherwise."
245 (with-slots ((exponents1 exponents))
246 m1
247 (with-slots ((exponents2 exponents))
248 m2
249 (with-slots ((exponents3 exponents))
250 m3
251 (every #'(lambda (x y z) (<= x (max y z)))
252 exponents1 exponents2 exponents3))))))
253
254(defgeneric lcm-divides-lcm-p (object1 object2 object3 object4)
255 (:method ((m1 monom) (m2 monom) (m3 monom) (m4 monom))
256 "Returns T if monomial LCM(M1,M2) divides LCM(M3,M4), NIL otherwise."
257 (with-slots ((exponents1 exponents))
258 m1
259 (with-slots ((exponents2 exponents))
260 m2
261 (with-slots ((exponents3 exponents))
262 m3
263 (with-slots ((exponents4 exponents))
264 m4
265 (every #'(lambda (x y z w) (<= (max x y) (max z w)))
266 exponents1 exponents2 exponents3 exponents4)))))))
267
268(defgeneric monom-lcm-equal-lcm-p (object1 object2 object3 object4)
269 (:method ((m1 monom) (m2 monom) (m3 monom) (m4 monom))
270 "Returns T if monomial LCM(M1,M2) equals LCM(M3,M4), NIL otherwise."
271 (with-slots ((exponents1 exponents))
272 m1
273 (with-slots ((exponents2 exponents))
274 m2
275 (with-slots ((exponents3 exponents))
276 m3
277 (with-slots ((exponents4 exponents))
278 m4
279 (every
280 #'(lambda (x y z w) (= (max x y) (max z w)))
281 exponents1 exponents2 exponents3 exponents4)))))))
282
283(defgeneric divisible-by-p (object1 object2)
284 (:documentation "Return T if OBJECT1 is divisible by OBJECT2.")
285 (:method ((m1 monom) (m2 monom))
286 "Returns T if monomial M1 is divisible by monomial M2, NIL otherwise."
287 (with-slots ((exponents1 exponents))
288 m1
289 (with-slots ((exponents2 exponents))
290 m2
291 (every #'>= exponents1 exponents2)))))
292
293(defgeneric rel-prime-p (object1 object2)
294 (:documentation "Returns T if objects OBJECT1 and OBJECT2 are relatively prime.")
295 (:method ((m1 monom) (m2 monom))
296 "Returns T if two monomials M1 and M2 are relatively prime (disjoint)."
297 (with-slots ((exponents1 exponents))
298 m1
299 (with-slots ((exponents2 exponents))
300 m2
301 (every #'(lambda (x y) (zerop (min x y))) exponents1 exponents2)))))
302
303(defgeneric universal-lcm (object1 object2)
304 (:documentation "Returns the multiple of objects OBJECT1 and OBJECT2.")
305 (:method ((m1 monom) (m2 monom))
306 "Returns least common multiple of monomials M1 and M2."
307 (with-slots ((exponents1 exponents))
308 m1
309 (with-slots ((exponents2 exponents))
310 m2
311 (let* ((exponents (copy-seq exponents1)))
312 (map-into exponents #'max exponents1 exponents2)
313 (make-instance 'monom :exponents exponents))))))
314
315
316(defgeneric universal-gcd (object1 object2)
317 (:documentation "Returns GCD of objects OBJECT1 and OBJECT2")
318 (:method ((m1 monom) (m2 monom))
319 "Returns greatest common divisor of monomials M1 and M2."
320 (with-slots ((exponents1 exponents))
321 m1
322 (with-slots ((exponents2 exponents))
323 m2
324 (let* ((exponents (copy-seq exponents1)))
325 (map-into exponents #'min exponents1 exponents2)
326 (make-instance 'monom :exponents exponents))))))
327
328(defgeneric depends-p (object k)
329 (:documentation "Returns T iff object OBJECT depends on variable K.")
330 (:method ((m monom) k)
331 "Return T if the monomial M depends on variable number K."
332 (declare (type fixnum k))
333 (with-slots (exponents)
334 m
335 (plusp (elt exponents k)))))
336
337(defgeneric left-tensor-product-by (self other)
338 (:documentation "Returns a tensor product SELF by OTHER, stored into
339 SELF. Return SELF.")
340 (:method ((self monom) (other monom))
341 (with-slots ((exponents1 exponents))
342 self
343 (with-slots ((exponents2 exponents))
344 other
345 (setf exponents1 (concatenate 'vector exponents2 exponents1))))
346 self))
347
348(defgeneric right-tensor-product-by (self other)
349 (:documentation "Returns a tensor product of OTHER by SELF, stored
350 into SELF. Returns SELF.")
351 (:method ((self monom) (other monom))
352 (with-slots ((exponents1 exponents))
353 self
354 (with-slots ((exponents2 exponents))
355 other
356 (setf exponents1 (concatenate 'vector exponents1 exponents2))))
357 self))
358
359(defgeneric left-contract (self k)
360 (:documentation "Drop the first K variables in object SELF.")
361 (:method ((self monom) k)
362 "Drop the first K variables in monomial M."
363 (declare (fixnum k))
364 (with-slots (exponents)
365 self
366 (setf exponents (subseq exponents k)))
367 self))
368
369(defun make-monom-variable (nvars pos &optional (power 1)
370 &aux (m (make-instance 'monom :dimension nvars)))
371 "Construct a monomial in the polynomial ring
372RING[X[0],X[1],X[2],...X[NVARS-1]] over the (unspecified) ring RING
373which represents a single variable. It assumes number of variables
374NVARS and the variable is at position POS. Optionally, the variable
375may appear raised to power POWER. "
376 (declare (type fixnum nvars pos power) (type monom m))
377 (with-slots (exponents)
378 m
379 (setf (elt exponents pos) power)
380 m))
381
382(defun make-monom-constant (dimension)
383 (make-instance 'monom :dimension dimension))
384
385;; pure lexicographic
386(defgeneric lex> (p q &optional start end)
387 (:documentation "Return T if P>Q with respect to lexicographic
388order, otherwise NIL. The second returned value is T if P=Q,
389otherwise it is NIL.")
390 (:method ((p monom) (q monom) &optional (start 0) (end (monom-dimension p)))
391 (declare (type fixnum start end))
392 (do ((i start (1+ i)))
393 ((>= i end) (values nil t))
394 (cond
395 ((> (monom-elt p i) (monom-elt q i))
396 (return-from lex> (values t nil)))
397 ((< (monom-elt p i) (monom-elt q i))
398 (return-from lex> (values nil nil)))))))
399
400;; total degree order, ties broken by lexicographic
401(defgeneric grlex> (p q &optional start end)
402 (:documentation "Return T if P>Q with respect to graded
403lexicographic order, otherwise NIL. The second returned value is T if
404P=Q, otherwise it is NIL.")
405 (:method ((p monom) (q monom) &optional (start 0) (end (monom-dimension p)))
406 (declare (type monom p q) (type fixnum start end))
407 (let ((d1 (total-degree p start end))
408 (d2 (total-degree q start end)))
409 (declare (type fixnum d1 d2))
410 (cond
411 ((> d1 d2) (values t nil))
412 ((< d1 d2) (values nil nil))
413 (t
414 (lex> p q start end))))))
415
416;; reverse lexicographic
417(defgeneric revlex> (p q &optional start end)
418 (:documentation "Return T if P>Q with respect to reverse
419lexicographic order, NIL otherwise. The second returned value is T if
420P=Q, otherwise it is NIL. This is not and admissible monomial order
421because some sets do not have a minimal element. This order is useful
422in constructing other orders.")
423 (:method ((p monom) (q monom) &optional (start 0) (end (monom-dimension p)))
424 (declare (type fixnum start end))
425 (do ((i (1- end) (1- i)))
426 ((< i start) (values nil t))
427 (declare (type fixnum i))
428 (cond
429 ((< (monom-elt p i) (monom-elt q i))
430 (return-from revlex> (values t nil)))
431 ((> (monom-elt p i) (monom-elt q i))
432 (return-from revlex> (values nil nil)))))))
433
434
435;; total degree, ties broken by reverse lexicographic
436(defgeneric grevlex> (p q &optional start end)
437 (:documentation "Return T if P>Q with respect to graded reverse
438lexicographic order, NIL otherwise. The second returned value is T if
439P=Q, otherwise it is NIL.")
440 (:method ((p monom) (q monom) &optional (start 0) (end (monom-dimension p)))
441 (declare (type fixnum start end))
442 (let ((d1 (total-degree p start end))
443 (d2 (total-degree q start end)))
444 (declare (type fixnum d1 d2))
445 (cond
446 ((> d1 d2) (values t nil))
447 ((< d1 d2) (values nil nil))
448 (t
449 (revlex> p q start end))))))
450
451(defgeneric invlex> (p q &optional start end)
452 (:documentation "Return T if P>Q with respect to inverse
453lexicographic order, NIL otherwise The second returned value is T if
454P=Q, otherwise it is NIL.")
455 (:method ((p monom) (q monom) &optional (start 0) (end (monom-dimension p)))
456 (declare (type fixnum start end))
457 (do ((i (1- end) (1- i)))
458 ((< i start) (values nil t))
459 (declare (type fixnum i))
460 (cond
461 ((> (monom-elt p i) (monom-elt q i))
462 (return-from invlex> (values t nil)))
463 ((< (monom-elt p i) (monom-elt q i))
464 (return-from invlex> (values nil nil)))))))
465
466(defun reverse-monomial-order (order)
467 "Create the inverse monomial order to the given monomial order ORDER."
468 #'(lambda (p q &optional (start 0) (end (monom-dimension q)))
469 (declare (type monom p q) (type fixnum start end))
470 (funcall order q p start end)))
471
472;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
473;;
474;; Order making functions
475;;
476;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
477
478;; This returns a closure with the same signature
479;; as all orders such as #'LEX>.
480(defun make-elimination-order-factory-1 (&optional (secondary-elimination-order #'lex>))
481 "It constructs an elimination order used for the 1-st elimination ideal,
482i.e. for eliminating the first variable. Thus, the order compares the degrees of the
483first variable in P and Q first, with ties broken by SECONDARY-ELIMINATION-ORDER."
484 #'(lambda (p q &optional (start 0) (end (monom-dimension p)))
485 (declare (type monom p q) (type fixnum start end))
486 (cond
487 ((> (monom-elt p start) (monom-elt q start))
488 (values t nil))
489 ((< (monom-elt p start) (monom-elt q start))
490 (values nil nil))
491 (t
492 (funcall secondary-elimination-order p q (1+ start) end)))))
493
494;; This returns a closure which is called with an integer argument.
495;; The result is *another closure* with the same signature as all
496;; orders such as #'LEX>.
497(defun make-elimination-order-factory (&optional
498 (primary-elimination-order #'lex>)
499 (secondary-elimination-order #'lex>))
500 "Return a function with a single integer argument K. This should be
501the number of initial K variables X[0],X[1],...,X[K-1], which precede
502remaining variables. The call to the closure creates a predicate
503which compares monomials according to the K-th elimination order. The
504monomial orders PRIMARY-ELIMINATION-ORDER and
505SECONDARY-ELIMINATION-ORDER are used to compare the first K and the
506remaining variables, respectively, with ties broken by lexicographical
507order. That is, if PRIMARY-ELIMINATION-ORDER yields (VALUES NIL T),
508which indicates that the first K variables appear with identical
509powers, then the result is that of a call to
510SECONDARY-ELIMINATION-ORDER applied to the remaining variables
511X[K],X[K+1],..."
512 #'(lambda (k)
513 (cond
514 ((<= k 0)
515 (error "K must be at least 1"))
516 ((= k 1)
517 (make-elimination-order-factory-1 secondary-elimination-order))
518 (t
519 #'(lambda (p q &optional (start 0) (end (monom-dimension p)))
520 (declare (type monom p q) (type fixnum start end))
521 (multiple-value-bind (primary equal)
522 (funcall primary-elimination-order p q start k)
523 (if equal
524 (funcall secondary-elimination-order p q k end)
525 (values primary nil))))))))
526
527(defclass term (monom)
528 ((coeff :initarg :coeff :initform 1 :accessor term-coeff :type ring))
529 (:default-initargs :coeff 1)
530 (:documentation "Implements a term, i.e. a product of a scalar
531and powers of some variables, such as 5*X^2*Y^3."))
532
533(defmethod shared-initialize :around ((self term) slot-names &rest initargs &key (coeff 1))
534 "A convenience method. If a coefficient is an integer, wrap it in the INTEGER-RING object"
535 ;; Dispatch on the type of supplied :COEFF arg
536 (typecase coeff
537 (integer
538 (setf (getf initargs :coeff) (make-instance 'integer-ring :value coeff))))
539 ;; Now pass new initargs to the next method
540 (apply #'call-next-method (list* self slot-names initargs)))
541
542
543(defmethod update-instance-for-different-class :after ((old monom) (new term) &key (coeff 1))
544 "Converts OLD of class MONOM to a NEW of class TERM, initializing coefficient to COEFF."
545 (reinitialize-instance new :coeff coeff))
546
547(defmethod update-instance-for-different-class :after ((old term) (new term) &key (coeff (term-coeff old)))
548 "Converts OLD of class TERM to a NEW of class TERM, initializing coefficient to COEFF."
549 (reinitialize-instance new :coeff coeff))
550
551
552(defmethod print-object ((self term) stream)
553 (print-unreadable-object (self stream :type t :identity t)
554 (with-accessors ((exponents monom-exponents)
555 (coeff term-coeff))
556 self
557 (format stream "EXPONENTS=~A COEFF=~A"
558 exponents coeff))))
559
560(defmethod copy-instance :around ((object term) &rest initargs &key &allow-other-keys)
561 "An :AROUND method of COPY-INSTANCE. It replaces the coefficient with a fresh copy."
562 (declare (ignore object initargs))
563 (let ((copy (call-next-method)))
564 (setf (term-coeff copy) (copy-instance (term-coeff object)))
565 copy))
566
567(defmethod multiply-by ((self term) (other number))
568 (reinitialize-instance self :coeff (multiply-by (term-coeff self) other)))
569
570(defmethod divide-by ((self term) (other number))
571 (reinitialize-instance self :coeff (divide-by (term-coeff self) other)))
572
573(defmethod unary-inverse :after ((self term))
574 (with-slots (coeff)
575 self
576 (setf coeff (unary-inverse coeff))))
577
578(defun make-term-constant (dimension &optional (coeff 1))
579 (make-instance 'term :dimension dimension :coeff coeff))
580
581(defmethod universal-equalp ((term1 term) (term2 term))
582 "Returns T if TERM1 and TERM2 are equal as MONOM, and coefficients
583are UNIVERSAL-EQUALP."
584 (and (call-next-method)
585 (universal-equalp (term-coeff term1) (term-coeff term2))))
586
587(defmethod multiply-by :before ((self term) (other term))
588 "Destructively multiply terms SELF and OTHER and store the result into SELF.
589It returns SELF."
590 (setf (term-coeff self) (multiply-by (term-coeff self) (term-coeff other))))
591
592
593(defmethod left-tensor-product-by :before ((self term) (other term))
594 (setf (term-coeff self) (multiply-by (term-coeff self) (term-coeff other))))
595
596(defmethod right-tensor-product-by :before ((self term) (other term))
597 (setf (term-coeff self) (multiply-by (term-coeff self) (term-coeff other))))
598
599(defmethod divide-by :before ((self term) (other term))
600 (setf (term-coeff self) (divide-by (term-coeff self) (term-coeff other))))
601
602(defmethod unary-minus ((self term))
603 (setf (term-coeff self) (unary-minus (term-coeff self)))
604 self)
605
606(defmethod universal-zerop ((self term))
607 (universal-zerop (term-coeff self)))
608
609(defgeneric ->list (self)
610 (:method ((self monom))
611 "A human-readable representation of a monomial SELF as a list of exponents."
612 (coerce (monom-exponents self) 'list))
613 (:method ((self term))
614 "A human-readable representation of a term SELF as a cons of the list of exponents and the coefficient."
615 (cons (coerce (monom-exponents self) 'list) (->sexp (term-coeff self)))))
616
617(defmethod ->sexp :before ((object monom) &optional vars)
618 "Check the length of variables VARS against the length of exponents in OBJECT."
619 (with-slots (exponents)
620 object
621 (assert (= (length vars) (length exponents))
622 nil
623 "Variables ~A and exponents ~A must have the same length." vars exponents)))
624
625(defmethod ->sexp ((object monom) &optional vars)
626 "Convert a monomial OBJECT to infix form, using variable VARS to build the representation."
627 (with-slots (exponents)
628 object
629 (let ((m (mapcan #'(lambda (var power)
630 (cond ((= power 0) nil)
631 ((= power 1) (list var))
632 (t (list `(expt ,var ,power)))))
633 vars (coerce exponents 'list))))
634 (cond ((endp m) 1)
635 ((endp (cdr m)) (car m))
636 (t
637 (cons '* m))))))
638
639(defmethod ->sexp :around ((object term) &optional vars)
640 "Convert a term OBJECT to infix form, using variable VARS to build the representation."
641 (declare (ignore vars))
642 (with-slots (coeff)
643 object
644 (let ((monom-sexp (call-next-method))
645 (coeff-sexp (->sexp coeff)))
646 (cond ((eql coeff-sexp 1) monom-sexp)
647 ((atom monom-sexp)
648 (cond ((eql monom-sexp 1) coeff-sexp)
649 (t (list '* coeff-sexp monom-sexp))))
650 ((eql (car monom-sexp) '*)
651 (list* '* coeff-sexp (cdr monom-sexp)))
652 (t
653 (list '* coeff-sexp monom-sexp))))))
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