Solution to SICP Exercise 1.36

Structure and Interpretation of Computer Programs

Solution to Exercise 1.36:

(define tolerance 0.00001)
(define (fixed-point f first-guess)
(define (close-enough? v1 v2)
(< (abs (- v1 v2)) tolerance))
(define (try guess)
(display guess)
(newline)
(let ((next (f guess)))
(if (close-enough? guess next)
next
(try next))))
(try first-guess))

(define (average a b) (/ (+ a b) 2))

(define result-with-damping
(fixed-point (lambda (x) (average x (/ (log 1000) (log x))))
2.0))

(display "result-with-damping: ")
(display result-with-damping)
(newline)
(newline)

(define result-without-damping
(fixed-point (lambda (x) (/ (log 1000) (log x)))
2.0))

(display "result-without-damping: ")
(display result-without-damping)

Output:

2.0
5.9828921423310435
4.922168721308343
4.628224318195455
4.568346513136242
4.5577305909237005
4.555909809045131
4.555599411610624
4.5555465521473675
result-with-damping: 4.555537551999825

2.0
9.965784284662087
3.004472209841214
6.279195757507157
3.759850702401539
5.215843784925895
4.182207192401397
4.8277650983445906
4.387593384662677
4.671250085763899
4.481403616895052
4.6053657460929
4.5230849678718865
4.577114682047341
4.541382480151454
4.564903245230833
4.549372679303342
4.559606491913287
4.552853875788271
4.557305529748263
4.554369064436181
4.556305311532999
4.555028263573554
4.555870396702851
4.555315001192079
4.5556812635433275
4.555439715736846
4.555599009998291
4.555493957531389
4.555563237292884
4.555517548417651
4.555547679306398
4.555527808516254
4.555540912917957
result-without-damping: 4.555532270803653

Solution to SICP Exercise 1.33

Structure and Interpretation of Computer Programs

Solution to Exercise 1.33:

(define (filtered-accumulate predicate combiner null-value term a next b)
(define (iter a result)
(if (> a b)
result
(iter (next a) (if (predicate a)
(combiner (term a) result)
result))))
(iter a null-value))

; part a
(define (square x) (* x x))

(define (sum-of-squared-primes a b)
(define (square-and-add i result) (+ (square i) result))
(filtered-accumulate prime? square-and-add 0 identity a inc b))

; part b
(define (product-of-positives-relatively-prime-to n)
(define (relatively-prime? i)
(= 1 (gcd i n)))
(filtered-accumulate relatively-prime? * 1 identity 1 inc (- n 1)))

Solution to SICP Exercise 1.32

Structure and Interpretation of Computer Programs

Solution to Exercise 1.32:

; part a (recursive process)

(define (accumulate-r combiner null-value term a next b)
(if (> a b)
null-value
(combiner (term a)
(accumulate-r combiner null-value term (next a) next b))))

(define (sum-r term a next b)
(accumulate-r + 0 term a next b))

(define (product-r term a next b)
(accumulate-r * 1 term a next b))

; part b (iterative process)

(define (accumulate-i combiner null-value term a next b)
(define (iter a result)
(if (> a b)
result
(iter (next a) (combiner result (term a)))))
(iter a null-value))

Solution to SICP Exercise 1.31

Structure and Interpretation of Computer Programs

Solution to Exercise 1.31:

; part a (recursive process)
(define (product-r term a next b)
(if (> a b)
1
(* (term a)
(product-r term (next a) next b))))

(define (identity i) i)
(define (inc i) (+ i 1))

(define (factorial n)
(product-r identity 1 inc n))

(define (pi-approximator terms)
(define (numerator i)
(+ i (if (odd? i) 1 2)))
(define (denominator i)
(+ i (if (odd? i) 2 1)))
(define (pi-term i)
(/ (numerator i) (denominator i)))
(* 4.0 (product-r pi-term 1 inc terms)))

; part b (iterative process)
(define (product-i term a next b)
(define (iter a result)
(if (> a b)
result
(iter (next a) (* result (term a)))))
(iter a 1))