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Re: Comparing 2 arrays [message #55669 is a reply to message #55557]

Tue, 28 August 2007 08:15

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Jean H. writes:

> to get back to a previous discussion we had a few month ago about being
> "sufficiently close to zero", shouldn't it be (data1.A - data2.B) LT
> epsilon * data1.A , with epsilon=(machar()).eps?

OK, I found that discussion and read it eight or ten times until
I finally understood it. (Probably why I forgot it before.)

I've put a significantly edited discussion of this
problem here:

http://www.dfanning.com/code_tips/comparearray.html

In my preferred solution now, I choose a number that
is "sufficiently close" to zero like this:

epsilon = (MACHAR()).eps
NUMBER = (array_1 > array_2) * epsilon

Then, the comparison between arrays is done like this:

IF Total(Abs(array_1 - array_2) LT NUMBER) EQ N_Elements(array_1) $
THEN RETURN, 1 ELSE RETURN, 0

Additional comments welcome if you want to argue further. :-)

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: Comparing 2 arrays By: David Fanning on Mon, 27 August 2007 08:06
		Re: Comparing 2 arrays By: Conor on Mon, 27 August 2007 06:48
		Re: Comparing 2 arrays By: David Fanning on Sun, 26 August 2007 09:43
		Re: Comparing 2 arrays By: Jean H. on Sun, 26 August 2007 08:40
		Re: Comparing 2 arrays By: David Fanning on Sun, 26 August 2007 07:32
		Re: Comparing 2 arrays By: airy.jiang on Sun, 26 August 2007 02:39
		Re: Comparing 2 arrays By: teich on Sat, 25 August 2007 22:25
		Re: Comparing 2 arrays By: David Fanning on Sat, 25 August 2007 21:47
		Re: Comparing 2 arrays By: David Fanning on Sat, 25 August 2007 21:45
		Re: Comparing 2 arrays By: David Fanning on Tue, 28 August 2007 08:15
		Re: Comparing 2 arrays By: James Kuyper on Mon, 27 August 2007 10:40
		Re: Comparing 2 arrays By: Paul Van Delst[1] on Mon, 27 August 2007 10:52

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