comp.lang.idl-pvwave archive: archive » Re: Sky is falling, maybe?

Home » Public Forums » archive » Re: Sky is falling, maybe?

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Sky is falling, maybe? [message #68231 is a reply to message #68230]

Thu, 08 October 2009 12:11

Foldy Lajos
Messages: 268
Registered: October 2001

Senior Member

On Thu, 8 Oct 2009, Lasse Clausen wrote:

> I find the following odd but maybe the sky is just falling and one of
> you guys can explain why this happens. Try running
>
> power = randomu(1001, 150)
> power[77+lindgen(10)*3] = 1e+7
> help, where(~finite(power))
> plot, power, yrange=[.1, 10]
> loadct, 12
> oplot, smooth(power, 12, /nan), thick=3, color=20
> oplot, smooth(power, 12), thick=3, color=120
> end
>
> On my machine
>
> IDL> print, !version
> { x86_64 linux unix linux 7.0 Oct 25 2007 64 64}
>
> I see a distinct difference in the SMOOTH output after the very uppy-
> downy bit of the data. It seems the documentation should be changed
> from
>
> SMOOTH should never be called without the NAN keyword if the input
> array may possibly contain NaN values.
>
> to
>
> SMOOTH should never be called without the NAN. Period.
>
> Again, maybe I'm missing something but the SMOOTH function seems like
> a pretty straight forward piece of code - without ever having seen it,
> of course - that leaves very little room for error. But by the same
> token we all know that "Every program has at least one bug and can be
> shortened by at least one instruction - from which, by induction - it
> can be shown that every program can be reduced to one instruction that
> doesn't work".
>
> So long
> Lasse
>

Yes, the sky is falling, again :-) Try with 'power=double(power)' and the
difference will disappear (randomu and 1e7 are too far apart for float).

smooth(...) and smooth(..., /nan) use different algorithms. The previous
one uses a sliding window, while the other does not (the sliding window
would give all NaNs after the first NaN).

regards,
lajos

Report message to a moderator

[Message index]

		Re: Sky is falling, maybe? By: Jean H. on Thu, 08 October 2009 13:21
		Re: Sky is falling, maybe? By: Foldy Lajos on Thu, 08 October 2009 13:01
		Re: Sky is falling, maybe? By: JohnSmith on Thu, 08 October 2009 12:50
		Re: Sky is falling, maybe? By: Jean H. on Thu, 08 October 2009 12:14
		Re: Sky is falling, maybe? By: Foldy Lajos on Thu, 08 October 2009 12:11
		Re: Sky is falling, maybe? By: JohnSmith on Thu, 08 October 2009 12:04

Previous Topic:	Sky is falling, maybe?
Next Topic:	Re: Nearest neighbors

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 20:04:23 PDT 2025

Total time taken to generate the page: 0.00413 seconds