simultaneous operation and swap

2 files changed, 49 insertions, 2 deletions

diff --git a/lecture1b.rkt b/lecture1b.rkt
index b03e64f..b6769b0 100644
--- a/lecture1b.rkt
+++ b/lecture1b.rkt
@@ -3,7 +3,35 @@
   (p))
 (define (test x y)
   (if (= 0 x) 0 y))
-(test 0 (p))
-1
+;; (test 0 (p))
 
+(define (sqrt-iter guess prev x)
+  (if (good-enough? guess prev)
+    guess
+    (sqrt-iter (improve guess x) guess x)))
 
+(define (abs x)
+  (if (> x 0) x (- x)))
+
+(define (good-enough? guess prev)
+  (and 
+    (> prev 0) 
+    (< (abs (- 1 (/ guess prev))) 0.001)))
+
+(define (improve guess x)
+  (/ (+ (/ x guess) guess) 2))
+
+(sqrt-iter 1 0 9.0)
+
+(define (cube-improve guess x) 
+  (/ 
+    (+ (/ x (* guess guess)) (* 2 guess))
+    3))
+    
+
+(define (cuberoot-iter guess prev x)
+  (if (good-enough? guess prev)
+    guess
+    (cuberoot-iter (cube-improve guess x) guess x)))
+
+(cuberoot-iter 1 0 8.0)
diff --git a/tree-recursion.rkt b/tree-recursion.rkt
new file mode 100644
index 0000000..031d40f
--- /dev/null
+++ b/tree-recursion.rkt
@@ -0,0 +1,19 @@
+#lang sicp
+(define (myfun n)
+  (cond ((< n 3) n)
+        (else (+ (myfun (- n 1))
+                 (* 2 (myfun (- n 2)))
+                 (* 3 (myfun (- n 3)))))))
+(myfun 11)
+
+(define (myfun2 n)
+  (define (mf i a b c)
+    (cond ((< n 3) n)
+          ((> i n) a)
+          (else (mf (+ i 1) 
+                    (+ a (* 2 b) (* 3 c))
+                    a
+                    b))))
+  (mf 3 2 1 0))
+
+(myfun 11)