我该如何分别从Numpy和Scipy中导入阶乘函数以查看哪个更快?
我已经通过“import math”从Python中导入了阶乘函数。但是,它对于Numpy和Scipy无效。
我已经通过“import math”从Python中导入了阶乘函数。但是,它对于Numpy和Scipy无效。
你可以这样导入它们:
In [7]: import scipy, numpy, math
In [8]: scipy.math.factorial, numpy.math.factorial, math.factorial
Out[8]:
(<function math.factorial>,
<function math.factorial>,
<function math.factorial>)
scipy.math.factorial
和numpy.math.factorial
似乎只是math.factorial
的别名/引用,即scipy.math.factorial is math.factorial
和numpy.math.factorial is math.factorial
都应该返回True
。
对于Ashwini的答案非常好,指出了scipy.math.factorial
、numpy.math.factorial
和math.factorial
是相同的函数。然而,我建议使用Janne提到的那个scipy.special.factorial
,因为它是不同的。来自scipy的这个函数可以接受np.ndarray
作为输入,而其他函数则不能。
In [12]: import scipy.special
In [13]: temp = np.arange(10) # temp is an np.ndarray
In [14]: math.factorial(temp) # This won't work
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-14-039ec0734458> in <module>()
----> 1 math.factorial(temp)
TypeError: only length-1 arrays can be converted to Python scalars
In [15]: scipy.special.factorial(temp) # This works!
Out[15]:
array([ 1.00000000e+00, 1.00000000e+00, 2.00000000e+00,
6.00000000e+00, 2.40000000e+01, 1.20000000e+02,
7.20000000e+02, 5.04000000e+03, 4.03200000e+04,
3.62880000e+05])
SciPy有函数scipy.special.factorial
(原名scipy.misc.factorial
)
>>> import math
>>> import scipy.special
>>> math.factorial(6)
720
>>> scipy.special.factorial(6)
array(720.0)
from numpy import prod
def factorial(n):
print prod(range(1,n+1))
from operator import mul
def factorial(n):
print reduce(mul,range(1,n+1))
或者完全不需要帮助:
def factorial(n):
print reduce((lambda x,y: x*y),range(1,n+1))
import numpy as np
def factorial(n):
return reduce((lambda x,y: x*y),range(1,n+1))
from timeit import Timer
from utils import factorial
import scipy
n = 100
# test the time for the factorial function obtained in different ways:
if __name__ == '__main__':
setupstr="""
import scipy, numpy, math
from utils import factorial
n = 100
"""
method1="""
factorial(n)
"""
method2="""
scipy.math.factorial(n) # same algo as numpy.math.factorial, math.factorial
"""
nl = 1000
t1 = Timer(method1, setupstr).timeit(nl)
t2 = Timer(method2, setupstr).timeit(nl)
print 'method1', t1
print 'method2', t2
print factorial(n)
print scipy.math.factorial(n)
method1 0.0195569992065
method2 0.00638914108276
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
Process finished with exit code 0
scipy.misc.factorial
的好处在于它仅对数组中最大的数计算一次阶乘,其余的阶乘作为副作用在该过程中计算。 - Antony Hatchkinsscipy.special.factorial
。 - lincolnfriasscipy.special.factorial
也可以使用伽马函数来估算值。 - Nathan Musoke