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Incorrect behavior of /NAN [message #30033]

Thu, 04 April 2002 07:40

K. Bowman
Messages: 330
Registered: May 2000

Senior Member

I tried to incite some interest in this last week, but had no takers,
so I'll try again. ;-)

I believe that the behavior of the TOTAL function is incorrect in
the case where all of the data are NaN and the /NAN keyword is set.

Here are several possible cases:

IDL> a = !values.f_nan
IDL> print, total([a, 1.0])
NaN
IDL> print, total([a, 1.0], /nan)
1.00000
IDL> print, total([a, a])
NaN
IDL> print, total([a, a], /nan)
0.00000

I believe that the last case is incorrect.

The documentation for /NAN says "Elements with the value NaN are treated
as missing data." In the last case there are no valid data, so how can
their sum be zero?

I think this is probably a simple error in the TOTAL algorithm.
Rather than computing the "sum of all the non-NaN values", it is
probably doing "set sum to zero and then add all non-Nan values".

For comparison, the MEAN function does not behave this way.

IDL> print, mean([a, 1.0])
NaN
IDL> print, mean([a, 1.0], /nan)
1.00000
IDL> print, mean([a, a])
NaN
IDL> print, mean([a, a], /nan)
NaN

Before I submit something (at least a question) to RSI, does anyone
have comments?

Ken Bowman

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[Message index]

		Incorrect behavior of /NAN By: K. Bowman on Thu, 04 April 2002 07:40
		Re: Incorrect behavior of /NAN By: Craig Markwardt on Sat, 06 April 2002 07:46
		Re: Incorrect behavior of /NAN By: Kenneth P. Bowman on Sat, 06 April 2002 06:28
		Re: Incorrect behavior of /NAN By: David Fanning on Fri, 05 April 2002 17:57
		Re: Incorrect behavior of /NAN By: James Kuyper on Fri, 05 April 2002 14:53
		Re: Incorrect behavior of /NAN By: K. Bowman on Fri, 05 April 2002 14:25
		Re: Incorrect behavior of /NAN By: Craig Markwardt on Fri, 05 April 2002 13:53
		Re: Incorrect behavior of /NAN By: Paul van Delst on Fri, 05 April 2002 07:35
		Re: Incorrect behavior of /NAN By: Paul van Delst on Thu, 04 April 2002 13:52
		Re: Incorrect behavior of /NAN By: K. Bowman on Mon, 15 April 2002 06:47
		Re: Incorrect behavior of /NAN By: noymer on Sun, 14 April 2002 18:32

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