Thanks! This works great.
On Tuesday, July 15, 2014 2:28:11 PM UTC-7, Matthew wrote:
>
> Use sympy.stats, not sympy.statistics
>
> In [1]: x, mu = symbols('x,mu', real=True)
>
> In [2]: sigma = symbols('sigma', positive=True)
>
> In [3]: from sympy.stats import *
>
> In [4]: X = Normal('X', mu, sigma)
>
> In [5]: moment?
> Type: function
> String form: <function moment at 0x7fc3fbbe2b18>
> File: /home/mrocklin/workspace/sympy/sympy/stats/rv_interface.py
> Definition: moment(X, n, c=0, condition=None, **kwargs)
> Docstring:
> Return the nth moment of a random expression about c i.e. E((X-c)**n)
> Default value of c is 0.
>
> Examples
> ========
>
> >>> from sympy.stats import Die, moment, E
> >>> X = Die('X', 6)
> >>> moment(X, 1, 6)
> -5/2
> >>> moment(X, 2)
> 91/6
> >>> moment(X, 1) == E(X)
> True
>
> In [6]: moment(X, 1)
> Out[6]: μ
>
> In [7]: moment(X, 2)
> Out[7]:
> 2 2
> μ + σ
>
> In [8]: moment(X, 3)
> Out[8]:
> 3 2
> μ + 3⋅μ⋅σ
>
> In [9]: moment(X, 4)
> Out[9]:
> 4 2 2 4
> μ + 6⋅μ ⋅σ + 3⋅σ
>
>
>
> On Tue, Jul 15, 2014 at 1:40 PM, Justin Vincent <just...@gmail.com
> <javascript:>> wrote:
>
>> Wanted to get the moments of a Normal distribution WRT mu and sigma, a la:
>>
>> http://en.wikipedia.org/wiki/Normal_distribution#Moments
>>
>> For starters, this outputs 1 for one for one crazy domains, and then
>> leaves the integral unevaluated on the rest of the domain. But it gets one,
>> so I'm cool with that.
>>
>> from sympy.statistics import Normal
>> from sympy import symbols, integrate
>> f = Normal(mu, sigma).pdf(x)
>> x, mu, sigma = symbols('x mu sigma')
>> integrate(f, (x,-oo, oo))
>>
>> Then when I get the first moment, it really starts to go crazy though,
>> and leaves it all indefinite:
>> integrate(f * x, (x, -oo, oo))
>>
>> What approach should I take here if I wanted to get those values cited in
>> wikipedia? Haven't used Sympy much before. Thanks in advance.
>>
>> Justin
>>
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