[Kst] [Kst-plot/kst] 5fdad6: Fix a bug in saving despike filters.

[Nicolas Brisset]

Hi,

The "activity level" of a signal is an empiric value computed as the product of the standard deviation of the signal with the number of reversals within a sliding window.

I used it a few years ago to do some pilot workload evaluations and it worked quite well. It correlates well with human intuition, even if the absolute value does not mean much in itself but relative variations are interesting. And it has the advantage of being a mathematical, qualitative value. You have to tune the parameters (window width and noise level, as noise can create many false reversals which pollute the signal) according to your signal, but in the end it can produce interesting results.

Attached to this mail is a plot where you will hopefully get a feeling of what it means. At the top you have the signal, then its activity then the number of reversals and finally the standard deviation. Activity is the product of the latter two.

The idea is the following:
- if you have mostly "noise" the amplitude is small and the resulting activity is small due to the standard deviation term (200 to 300 s area in the plot)
- if you have large changes with slow dynamics, the product is small due to a low number of reversals (see smaller peaks around 1550 and 1580 s in the plot, compared to the larger peak at 1505 s)
- if the signal has large amplitudes and frequent direction changes, it means that there is a lot of activity (see around 1320 s, 1350 and 1505 s)

Recently a colleague asked me for something similar so I thought I should revive it :-) I hope it can be useful to someone else too.
I'll commit it in the coming minutes, when I've checked that the code is clean.

Nicolas

P.S.: 1) if you have a better name, we can change it. I originally considered "workload" but I found it even worse.
2) I have tried 2 approaches for the denoising, one is commented out in the code but feel free to test it and change the implementation if results are better.

----- Mail original -----
> De: "Barth Netterfield" <barth.netterfield at utoronto.ca>
> À: kst at kde.org
> Envoyé: Mardi 19 Novembre 2013 22:57:24
> Objet: Re: [Kst] [Kst-plot/kst] 5fdad6: Fix a bug in saving despike	filters.
> 
> What is the "activity level of a signal"?
> 
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