On Fri, Oct 15, 2010 at 1:00 PM, Raymond Hettinger
<raymond.hettinger@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-un...
[2]: http://www.reddit.com/r/programming/comments/ccbja/math_library_functions_th...
Geremy Condra
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