Changeset 1060

Timestamp:

2015-06-10T09:01:41-07:00 (10 years ago)

Author:

Marek Rychlik

Message:

* empty log message *

File:

• branches/f4grobner/.junk/poly-eval.lisp (modified) (1 diff)

branches/f4grobner/.junk/poly-eval.lisp

@@ +1 @@
+(defun alist-form (plist vars)
+  "Translates an expression PLIST, which should be a list of polynomials
+in variables VARS, to an alist representation of a polynomial.
+It returns the alist. See also PARSE-TO-ALIST."
+  (cond
+   ((endp plist) nil)
+   ((eql (first plist) '[)
+    (cons '[ (mapcar #'(lambda (x) (alist-form x vars)) (rest plist))))
+   (t
+    (assert (eql (car plist) '+))
+    (alist-form-1 (rest plist) vars))))
+
+(defun alist-form-1 (p vars
+                         &aux (ht (make-hash-table
+                                   :test #'equal :size 16))
+                         stack)
+  (dolist (term p)
+    (assert (eql (car term) '*))
+    (incf  (gethash (powers (cddr term) vars) ht 0) (second term)))
+  (maphash #'(lambda (key value) (unless (zerop value)
+                                   (push (cons key value) stack))) ht)
+  stack)
+    
+(defun powers (monom vars
+                     &aux (tab (pairlis vars (make-list (length vars)
+                                                        :initial-element 0))))
+  (dolist (e monom (mapcar #'(lambda (v) (cdr (assoc v tab))) vars))
+    (assert (equal (first e) '^))
+    (assert (integerp (third e)))
+    (assert (= (length e) 3))
+    (let ((x (assoc (second e) tab)))
+      (if (null x) (error "Variable ~a not in the list of variables." 
+                         (second e))
+        (incf (cdr x) (third e))))))
+  
+
+
 (defun convert-number (number-or-poly n)
   "Returns NUMBER-OR-POLY, if it is a polynomial. If it is a number,