further cleanup

Author: Trashtalk217

contents/thomas_algorithm/code/clisp/thomas.lisp

@@ -1,18 +1,20 @@
 ;;;; Thomas algorithm implementation in Common Lisp
 
+(defun div-set (number divisor)
+  (setf number (/ number divisor)))
+
 (defun thomas (diagonal-a diagonal-b diagonal-c last-column)
   "Returns the solutions to a tri-diagonal matrix non-destructively"
+  ;; we copy the inputs to ensure non-destructiveness
   (let ((a (copy-seq diagonal-a))
          (b (copy-seq diagonal-b))
          (c (copy-seq diagonal-c))
          (d (copy-seq last-column)))
-    (setf (svref c 0) (/ (svref c 0) (svref b 0)))
-    (setf (svref d 0) (/ (svref d 0) (svref b 0)))
+    (div-set (svref c 0) (svref b 0))
+    (div-set (svref d 0) (svref b 0))
     (loop
       for i from 1 upto (1- (length a)) do
-      (setf
-        (svref c i)
-        (/ (svref c i) (- (svref b i) (* (svref a i) (svref c (1- i))))))
+      (div-set (svref c i) (- (svref b i) (* (svref a i) (svref c (1- i)))))
       (setf
         (svref d i)
         (/
@@ -28,4 +30,5 @@
 (defparameter diagonal-c #(4 5 0))
 (defparameter last-column #(7 5 3))
 
+;; should print 0.8666667 1.5333333 -0.26666668
 (format t "~{~f ~}" (coerce (thomas diagonal-a diagonal-b diagonal-c last-column) 'list))