Implement 2.94

ex-2_77-97.scm

@@ -986,6 +986,22 @@
         (else (=zero?-terms (rest-terms terms)))))
     (=zero?-terms (term-list p)))
 
+  (define (remainder-terms a b)
+    (cdr (div-terms a b)))
+
+  (define (gcd-terms a b)
+    (if (empty-termlist? b)
+        a
+        (gcd-terms b (remainder-terms a b))))
+
+  (define (gcd-poly p1 p2)
+    (if (same-variable? (variable p1) (variable p2))
+        (make-poly (variable p1)
+                   (gcd-terms (term-list p1)
+                              (term-list p2)))
+        (error "Polys not in same var -- ADD-POLY"
+               (list p1 p2))))
+
   ;; interface to rest of the system
   (define (tag p) (attach-tag 'polynomial p))
   (put 'add '(polynomial polynomial)
@@ -996,6 +1012,8 @@
        (lambda (p1 p2) (tag (sub-poly p1 p2))))
   (put 'div '(polynomial polynomial)
        (lambda (p1 p2) (div-poly p1 p2)))
+  (put 'greatest-comond-divisor '(polynomial polynomial)
+       (lambda (p1 p2) (tag (gcd-poly p1 p2))))
   (put '=zero? '(polynomial) =zero?-poly)
   (put 'make 'poly-sparse
        (lambda (var terms) (tag (make-poly-sparse var terms))))
@@ -1071,3 +1089,9 @@
 
 (display "\nex-2.94 - polynomial gcd\n")
 
+(define (greatest-common-divisor x y) (apply-generic 'greatest-comond-divisor x y))
+(define p1 (make-poly-sparse 'x '((4 1) (3 -1) (2 -2) (1 2))))
+(define p2 (make-poly-sparse 'x '((3 1) (1 -1))))
+(display (greatest-common-divisor p1 p2)) (newline)
+
+(display "\nex-2.95\n")