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Re: IDL 8.2.2 and PLOT with NaN values [message #83696 is a reply to message #83679]

Wed, 27 March 2013 14:39

Lajos Foldy
Messages: 176
Registered: December 2011

Senior Member

On Wednesday, March 27, 2013 10:10:23 PM UTC+1, wlandsman wrote:
> Not only are the math errors hardware dependent, but today I came across the fact that it can depend on how the array is ordered.
>
> IDL> print,min([2.,!values.f_nan,3.])
> 2.00000
> IDL> print,min([!values.f_nan,3.,2.])
> NaN
> IDL> print,!version
> { x86_64 linux unix linux 8.2.2 Jan 23 2013 64 64}
>
> The help for MIN says
>
> "Note: If the MIN function is run on an array containing NaN values and the NAN keyword is not set, an invalid result will occur."
>
> but this should probably read
>
> Note: If the MIN function is run on an array containing NaN values and the NAN keyword is not set, an invalid result **may** occur.

This can be explained: a MIN function implementation may look like:

min=arr[0]
for j=1,n_elements(arr)-1 do min=min<arr[j]

so a non-NaN first elements is vital (without /NaN). For small arrays, only this first element counts. For large arrays, multithreading comes into the picture and there are multiple first elements (each thread has one somewhere in the array).

regards,
Lajos

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[Message index]

		Re: IDL 8.2.2 and PLOT with NaN values By: chris_torrence@NOSPAM on Fri, 29 March 2013 08:36
		Re: IDL 8.2.2 and PLOT with NaN values By: Lajos Foldy on Wed, 27 March 2013 14:39
		Re: IDL 8.2.2 and PLOT with NaN values By: wlandsman on Wed, 27 March 2013 14:10
		Re: IDL 8.2.2 and PLOT with NaN values By: Karlo Janos on Wed, 27 March 2013 03:08
		Re: IDL 8.2.2 and PLOT with NaN values By: Fabzi on Wed, 27 March 2013 02:39
		Re: IDL 8.2.2 and PLOT with NaN values By: Karlo Janos on Wed, 27 March 2013 01:21
		Re: IDL 8.2.2 and PLOT with NaN values By: Michael Galloy on Tue, 26 March 2013 11:21
		Re: IDL 8.2.2 and PLOT with NaN values By: Karlo Janos on Tue, 26 March 2013 10:05
		Re: IDL 8.2.2 and PLOT with NaN values By: Fabzi on Tue, 26 March 2013 09:44
		Re: IDL 8.2.2 and PLOT with NaN values By: Karlo Janos on Tue, 02 April 2013 00:13

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