小编hac*_*rb9的帖子

我正在a**16使用scipy-0.17 进行简单的稀疏矩阵求幂.(注意,不是逐元素乘法).但是,在我的机器上(运行Debian stable和Ubuntu LTS),这比使用for循环或做一些愚蠢的事情慢十倍a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a.这没有意义,所以我假设我做错了什么,但是什么？

import scipy.sparse
from time import time

a=scipy.sparse.rand(2049,2049,.002)

print ("Trying exponentiation (a**16)")
t=time()
x=a**16
print (repr(x))
print ("Exponentiation took %f seconds\n" % (time()-t))

print ("Trying expansion (a*a*a*...*a*a)")
t=time()
y=a*a*a*a*a*a*a*a*a*a*a*a*a*a*a*a
print (repr(y))
print ("Expansion took %f seconds\n" % (time()-t))

print ("Trying a for loop (z=z*a)")
t=time()
z=scipy.sparse.eye(2049)
for i in range(16):
    z=z*a
print (repr(z))
print ("Looping took %f seconds\n" % (time()-t))

# Sanity check, all approximately the same answer, right? 
assert (abs(x-z)>=1e-9).nnz==0 …