2016 Update

Task/Euler-method/Common-Lisp/euler-method-1.lisp

@@ -7,8 +7,8 @@
 (defun euler (f y0 a b h)
 
   ;; Set the initial values and increments of the iteration variables.
-  (do ((t a  (incf t h))
-       (y y0 (incf y (* h (funcall f t y)))))
+  (do ((t a  (+ t h))
+       (y y0 (+ y (* h (funcall f t y)))))
 
       ;; End the iteration when t reaches the end b of the time interval.
       ((>= t b) 'DONE)

Task/Euler-method/Common-Lisp/euler-method-2.lisp

@@ -0,0 +1,13 @@
+;; slightly more idiomatic Common Lisp version
+
+(defun newton-cooling (time temperature)
+  "Newton's cooling law, f(t,T) = -0.07*(T-20)"
+  (declare (ignore time))
+  (* -0.07 (- temperature 20)))
+
+(defun euler (f y0 a b h)
+  "Euler's Method.
+Approximates y(time) in y'(time)=f(time,y) with y(a)=y0 and t=a..b and the step size h."
+  (loop for time from a below b by h
+        for y = y0 then (+ y (* h (funcall f time y)))
+        do (format t "~6,3F  ~6,3F~%" time y)))