[SciPy-user] multivariate distributions

Christopher Fonnesbeck fonnesbeck at mac.com
Wed Jun 2 08:01:48 CDT 2004

On Jun 2, 2004, at 1:57 AM, Scott Bray wrote:

> G'day Robert,
> i was kinda hoping you'd reply - you helped me out a little while ago. 
> well my project's sinced progressed and i've hit another problem. hope 
> you dont mind if i pick your brain again...
> i've done some wide reading and have found lots of info on multivarite 
> normal dists and some equations for the joint density of a 
> multivariate normal, but it doesn't seem useable to me. i have 5 lots 
> of N observations but the multinormal needs means and covariances 
> which i have been calculating FROM the functions (i did this using the 
> cauchy). i have heard about multivariate cauchy's but haven't been 
> able to find any concrete info.
> so my question is - how do i 'derive the formula on paper first'?

I'm not sure how a cauchy is going to help you get at a multivariate 
normal distribution. Are your data overdispersed, or something? Most 
statistics texts will give you the pdf of a multivariate normal; you 
just have to code that into python. I have a multivariate normal and 
wishart (i.e. multivariate gamma) programmed in FORTRAN and compiled as 
a python module using f2py, if you want it.

The rv module in scipy.stats has a multivariate_normal function, but 
this simply generates random variables.


Christopher J. Fonnesbeck ( c h r i s @ f o n n e s b e c k . o r g )
Georgia Cooperative Fish & Wildlife Research Unit, University of Georgia

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