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