On Jul 8, 2:24 am, Paul Rubin <http://phr...@nospam.invalid> wrote: > pdpi <pdpinhe...@gmail.com> writes: > > while abs(func(guess) - target) > epsilon: > > guess = (lo + hi) / 2. > > if sense * func(guess) > sense * target: > > hi = guess > > elif sense * func(guess) < sense * target: > > lo = guess > > elif lo == hi: > > return None > > return guess > > That is completely confusing. I get the, er, impression that "sense" > is supposed to change during the loop, and it takes much head > scratching to tell whether what you have there is right or not. Also, > it calls func 3 times on each loop, which could be extremely slow. > You don't know what func does, so eliminating 2/3 of the calls to it > is not a micro-optimization--it could be a major time saving. > > Yet another version: > > def _binary_search(x0, x1, func, target, epsilon): > y0,y1 = func(x0), func(x1) > while abs(y1 - target) > epsilon: > if x0 == x1 or cmp(y0,target) == cmp(y1,target): > return None > xn = (x0 + x1) / 2. > yn = func(xn) > if cmp(yn,target) == cmp(y0,target): > x0,y0 = xn,yn > else: > x1,y1 = xn,yn > return x1
micro-optimization was perhaps too harsh, but it is an optimization that's not obvious for the newbie, and one best learnt from experience rather than having it spoon fed. I'll restate: you should start with the cleanest code possible and mangle it for performance. Then again, that implicitly assumes that f(x) is more readable than y, which is really a matter of taste... -- http://mail.python.org/mailman/listinfo/python-list
