[PD] variance from mapping library

Mathieu Bouchard matju at artengine.ca
Mon Mar 23 21:04:22 CET 2009


On Mon, 23 Mar 2009, Mathieu Bouchard wrote:

> You can send simple repeated sequences to [mapping/variance] to show 
> that not only it can drift in the negative values almost endlessly, but 
> it doesn't even compute the variance of N values. This is because there 
> is a moving average of something involving another moving average. This 
> makes a global moving average of 2N-1 values instead of N, and then the 
> window isn't rectangular anymore, it's triangular, because different 
> values are counted different number of times depending on how old they 
> are.

errata: i mean that a moving average of a moving average is another moving 
average with a different window (the convolution of the two windows), but 
the case of [mapping/variance] is more complicated because of the extra 
operations being done, and so there is no easy way to describe it, but you 
can see that it uses too many values in the same way that the moving 
average of the moving average does.

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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal, Québec


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