On Sat, Oct 16, 2010 at 8:05 AM, geremy condra <debat...@gmail.com> wrote: > On Fri, Oct 15, 2010 at 1:00 PM, Raymond Hettinger > <raymond.hettin...@gmail.com> wrote: >> Hello guys. If you don't mind, I would like to hijack your thread :-) >> >> ISTM, that the minmax() idea is really just an optimization request. >> A single-pass minmax() is easily coded in simple, pure-python, >> so really the discussion is about how to remove the loop overhead >> (there isn't much you can do about the cost of the two compares >> which is where most of the time would be spent anyway). >> >> My suggestion is to aim higher. There is no reason a single pass >> couldn't also return min/max/len/sum and perhaps even other summary >> statistics like sum(x**2) so that you can compute standard deviation >> and variance. > > +1 from me. Here's a normal cdf and chi squared cdf approximation I > use for randomness testing. They may need to refined for inclusion, > but you're welcome to use them if you'd like. > > from math import sqrt, erf > > def normal_cdf(x, mu=0, sigma=1): > """Approximates the normal cumulative distribution""" > return (1/2) * (1 + erf((x+mu)/(sigma*sqrt(2)))) > > def chi_squared_cdf(x, k): > """Approximates the cumulative chi-squared statistic with k degrees > of freedom.""" > numerator = 1 - (2/(9*k)) - ((x/k)**(1/3)) > denominator = (1/3) * sqrt(2/k) > return normal_cdf(numerator/denominator) > >> A few years ago, Guido and other python devvers supported a >> proposal I made to create a stats module, but I didn't have time >> to develop it. The basic idea was that python's batteries should >> include most of the functionality available on advanced student >> calculators. Another idea behind it was that we could invisibility >> do-the-right-thing under the hood to help users avoid numerical >> problems (i.e. math.fsum(s)/len(s) is a more accurate way to >> compute an average because it doesn't lose precision when >> building-up the intermediate sums). > > Can you give some other examples? Sage does some of this and I > frequently find it annoying, actually, but I'm not sure if you're > referring to the same things there. have seen a blog post[1] several months ago from reddit[2], maybe it worth a reading. [1]: http://www.johndcook.com/blog/2010/06/07/math-library-functions-that-seem-unnecessary/ [2]: http://www.reddit.com/r/programming/comments/ccbja/math_library_functions_that_seem_unnecessary/
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