语句执行时间比较

>>> timeit np.dot(np.array([1,2,3]),np.array([1,2,3]))
>>>The slowest run took 5.85 times longer than the fastest. This could mean that an intermediate result is being cached
        100000 loops, best of 3: 4.74 µs per loop

>>>timeit np.dot([1,2,3],np.array([1,2,3]))
>>>The slowest run took 7.57 times longer than the fastest. This could mean that an intermediate result is being cached
        100000 loops, best of 3: 4.67 µs per loop


这两句到底哪个耗时少点

没有用过timeit. 网上有人提问得到如下回应:

The message "intermediate result is being cached" is just a blind guess in the canned message reported by %timeit. It may or may not be true, and you should not assume it is correct.


In particular, one of the most common reasons for the first run being slowest is that the array is in the CPU cache only after the first run.

CPUs cache things automatically; you cannot avoid this, and you don't really want to avoid it. However, optimizing algorithms so that CPU caches can work optimally is nowadays one of the bottlenecks that high-performance computing needs to take into account.

意思大致是说第一句的那个时间可以忽略, 是由于CPU缓存多用了一点时间.
从后面的时间看. 应该是第二个语句耗时少点.

whydo1 发表于 2016-10-13 20:11
没有用过timeit. 网上有人提问得到如下回应:

The message "intermediate result is being cached" is just ...

哦，好的，我知道了，多谢