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[Weaver]

[burakkucat]

My first (and currently only) suggestion is to restrict the domain of the X-axis values to be considered. I would use:

100 > X > 32

[Weaver]

[burakkucat]

As 100 - 32 = 68, my next suggestion is to perform an initial pass looking at blocks of 4. That should minimise the distraction caused by a pilot tone, etc.

(Why blocks of 4? No real reason other than that 4 x 17 = 68 and 4 > 1.)

I feel the urge to type "first differential".

[Weaver]

[burakkucat]

Just differentiate the arithmetic mean and find the turning point(s) of the curve. If you have a local maximum, followed by a local minimum, followed by a local maximum then the hollow curve phenomenon has struck again.

Hmm . . . I think you will need to look at the second differential. (My memory of A-level pure mathematics, from 50+ years ago, has faded somewhat.)

[Weaver]

I understand the calculus rationale. However the pilot tone thing has a huge spike in both first and second derivatives.

l would rather not do differentiation; recte finite differences here, since the bits-per-bin data are discrete integer-valued (y). The reason is because having a loop with lots of subtractions in it will be slow, as Shortcuts is incredibly slow.

What were you saying before about four quarters? My most urgent need is to get rid of all spikes, pilot tone being the main one. Wobble of y +/- 1 is also a nuisance, some being mere quantisation noise.

[burakkucat]

I'm not too sure what I was thinking about, late yesterday. 

At the moment, I can't see a clear forward path to a boolean answer to a query asking if a "hollow curve" is present.

Random thought. Suppose that the bit loading per sub-carrier index is "harvested", once, at the same time each 24 hour period. Now subtract that of day_n from that of day_n+1 to give the delta on day_n+1. What would that delta show when the "hollow curve phenomenon" first appears?

[Weaver]

[burakkucat]

I was thinking about a crude spike detector that looks at x==60 for a dip down to y=2 (or maybe 3,4 for a bit of insurance) and then if it sees one at x==60 it walks sideways in increasing x+=2 to get away from the spike. Then y[x==60 or 62] now is compared against y[40] and y[85] as mentioned in my first post. Something like

        hollow = y[x==60 or 62] < y[40] && y[x==60 or 62] < y[85];

I am not that certain . . . but it certainly is worth testing.

[Weaver]

[Weaver]

[Weaver]

[jelv]

A question: when writing posts in the forums, it does of course go crackers when I try to write certain things inside [ ]. How do I work around that?

Enclose the text in [nobbc]...[/nobbc] tags (which I had to do in this post so they would show - start a quote of this post to see how).

[burakkucat]