Ok, I will keep in mind numpy integration (and I do agree n-1 and n are virtually the same for large n). I am not sure I would be useful for statistics functionality, as my interests are in algebra, number theory and combinatorics, but I will try to help.
On Wed, Sep 14, 2011 at 11:23 AM, Ronan Lamy <[email protected]> wrote: > Le mercredi 14 septembre 2011 à 08:47 -0500, Matthew Rocklin a écrit : > > Hi Srinivas, > > > > > > Nice catch. I agree that it would be better if variance was defined in > > terms of n-1 rather than n. This seems like an easy fix to get started > > with SymPy if you'd like to try. There is a wiki page providing tips > > for the Development Workflow if you're not already familiar with git > > and such. > > > > > > If you're interested in improving the statistics functionality in > > SymPy let me know. This has been a project of mine. > > > > > > Best, > > -Matt > > > > On Tue, Sep 13, 2011 at 10:06 PM, Srinivas <[email protected]> wrote: > > Hi, > > I wanted to join as a new developer of sympy, so I am > > looking > > through the code to get familiar with it. > > For /sympy/sympy/statistics/ > > distributions.py, the Sample class defines the variance to be: > > s.variance = sum([(x-mean)**2 for x in s]) / Integer(len(s)) > > > > But, this would be the biased estimator. My question is > > would/should > > this class use the unbiased estimator (replacing > > Integer(len(s)) with > > Integer(len(s)-1))? > > The so-called "unbiased estimator" (dividing by n-1) isn't necessarily > meaningful. Dividing by n at least always gives the second central > moment of the sample distribution. It's also the default in numpy (cf. > > http://docs.scipy.org/doc/numpy-1.6.0/reference/generated/numpy.std.html#numpy.std), > so I think we should stay consistent with that. > > Besides, I don't think that the Sample class is actually usable as it > exists currently (doesn't work correctly with symbolic or non-real > arguments, computes everything up-front, ...) and I don't even > understand what its purpose is. Fixing this would be much more useful. > > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
