combine lists (like vectors) and calculate sum of pairwise differences (= 'cost')

decons.lisp

@@ -7,6 +7,7 @@
            #:absv #:double #:remainder
            #:scalar-p #:tensor #:at
            #:rapply #:rreduce
+           #:combine #:cost
            #:line
            #:lgx
            ))
@@ -87,6 +88,21 @@
   (:method (op (v list) &key (initial-value 0)) 
     (rreduce op v :initial-value initial-value)))
 
+;;;; combine
+
+(defun combine (l1 l2)
+  (mapcar (lambda (x) (scons (pop l1) x)) l2))
+
+(defgeneric scons (a b)
+  (:method (a b) (list a b))
+  (:method (a (b list)) (cons a b)))
+
+;;;; cost calculation
+
+(defun cost (have want)
+  (reduce #'+ 
+          (mapcar (lambda (p) (abs (apply #'- p))) 
+                  (combine have want))))
 
 ;;;; logging (printing) functions for debugging purposes
 

test-decons.lisp

@@ -13,6 +13,7 @@
     (test-basic)
     (test-tensor)
     (test-rapply)
+    (test-rreduce)
     (test-line)
     (t:show-result)))
 
@@ -45,6 +46,10 @@
   (== (decons:rapply #'- '(6 7) '(4 5)) '((2 3) (1 2))) 
 )
 
+(deftest test-rreduce ()
+  (== (decons:rreduce #'+ '(1 2 (3 4))) 10)
+)
+
 (deftest test-line ()
   (let ((p1 (decons:line 0.0))
         (p2 (decons:line 1.0))
@@ -55,4 +60,6 @@
     (== (funcall p2 '(0.5 2.0)) 2.5)
     (setf ps1 (decons:line (car ds1)))
     (== (funcall ps1 '(0.5 2.0)) '(3.0 2.5 4.0 3.5))
+    (== (funcall ps1 '(1.0 0.0)) '(2.0 1.0 4.0 3.0))
+    (== (decons:cost (funcall ps1 '(1.0 0.0)) (cadr ds1)) 0.899999861)
 ))