The article is comparing to the dynamic programming algorithm, which requires reading and writing to an array or hash table (the article uses a hash table, which is slower).
The naive algorithm is way faster than the DP algorithm.
It’s not that hard to check yourself. Running the following code on my machine, I get that the linear algebra algorithm is already faster than the naive algorithm at around n = 100 or so. I’ve written a more optimised version of the naive algorithm, which is beaten somewhere between n = 200 and n = 500.
Try running this Python code on your machine and see what you get:
import timeit
deffib_naive(n):
a = 0
b = 1while0 < n:
b = a + b
a = b - a
n = n - 1return a
deffib_naive_opt(n):
a, b = 0, 1for _ inrange(n):
a, b = b + a, b
return a
defmatmul(a, b):
return (
(a[0][0] * b[0][0] + a[0][1] * b[1][0], a[0][0] * b[0][1] + a[0][1] * b[1][1]),
(a[1][0] * b[0][0] + a[1][1] * b[1][0], a[1][0] * b[0][1] + a[1][1] * b[1][1]),
)
deffib_linear_alg(n):
z = ((1, 1), (1, 0))
y = ((1, 0), (0, 1))
while n > 0:
if n % 2 == 1:
y = matmul(y, z)
z = matmul(z, z)
n //= 2return y[0][0]
deftime(func, n):
times = timeit.Timer(lambda: func(n)).repeat(repeat=5, number=10000)
returnmin(times)
for n in (50, 100, 200, 500, 1000):
print("========")
print(f"n = {n}")
print(f"fib_naive:\t{time(fib_naive, n):.3g}")
print(f"fib_naive_opt:\t{time(fib_naive_opt, n):.3g}")
print(f"fib_linear_alg:\t{time(fib_linear_alg, n):.3g}")
Here’s what it prints on my machine:
========
n = 50
fib_naive: 0.0296fib_naive_opt: 0.0145fib_linear_alg: 0.0701
========
n = 100
fib_naive: 0.0652fib_naive_opt: 0.0263fib_linear_alg: 0.0609
========
n = 200
fib_naive: 0.135fib_naive_opt: 0.0507fib_linear_alg: 0.0734
========
n = 500
fib_naive: 0.384fib_naive_opt: 0.156fib_linear_alg: 0.112
========
n = 1000
fib_naive: 0.9fib_naive_opt: 0.347fib_linear_alg: 0.152
The article is comparing to the dynamic programming algorithm, which requires reading and writing to an array or hash table (the article uses a hash table, which is slower).
The naive algorithm is way faster than the DP algorithm.
It’s not that hard to check yourself. Running the following code on my machine, I get that the linear algebra algorithm is already faster than the naive algorithm at around n = 100 or so. I’ve written a more optimised version of the naive algorithm, which is beaten somewhere between n = 200 and n = 500.
Try running this Python code on your machine and see what you get:
import timeit def fib_naive(n): a = 0 b = 1 while 0 < n: b = a + b a = b - a n = n - 1 return a def fib_naive_opt(n): a, b = 0, 1 for _ in range(n): a, b = b + a, b return a def matmul(a, b): return ( (a[0][0] * b[0][0] + a[0][1] * b[1][0], a[0][0] * b[0][1] + a[0][1] * b[1][1]), (a[1][0] * b[0][0] + a[1][1] * b[1][0], a[1][0] * b[0][1] + a[1][1] * b[1][1]), ) def fib_linear_alg(n): z = ((1, 1), (1, 0)) y = ((1, 0), (0, 1)) while n > 0: if n % 2 == 1: y = matmul(y, z) z = matmul(z, z) n //= 2 return y[0][0] def time(func, n): times = timeit.Timer(lambda: func(n)).repeat(repeat=5, number=10000) return min(times) for n in (50, 100, 200, 500, 1000): print("========") print(f"n = {n}") print(f"fib_naive:\t{time(fib_naive, n):.3g}") print(f"fib_naive_opt:\t{time(fib_naive_opt, n):.3g}") print(f"fib_linear_alg:\t{time(fib_linear_alg, n):.3g}")
Here’s what it prints on my machine:
======== n = 50 fib_naive: 0.0296 fib_naive_opt: 0.0145 fib_linear_alg: 0.0701 ======== n = 100 fib_naive: 0.0652 fib_naive_opt: 0.0263 fib_linear_alg: 0.0609 ======== n = 200 fib_naive: 0.135 fib_naive_opt: 0.0507 fib_linear_alg: 0.0734 ======== n = 500 fib_naive: 0.384 fib_naive_opt: 0.156 fib_linear_alg: 0.112 ======== n = 1000 fib_naive: 0.9 fib_naive_opt: 0.347 fib_linear_alg: 0.152
Nice.
I have successfully stuck my foot in my own mouth.