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Re: Comparing 2 arrays [message #55664 is a reply to message #55564]

Tue, 28 August 2007 09:20

Jean H.
Messages: 472
Registered: July 2006

Senior Member

perfect!! ... we had to move all the equipment form our lab so I
couldn't participate in the debate (never send a post on Sunday if you
don't know what you will be doing on Monday :-)

Thanks all for the clarity of the answer/article!

David, in your example (in this message), you use
NUMBER = (array_1 > array_2) * epsilon
and
NUMBER = (array_1 > array_2) * epsilon * 2 in your article...

Also, but that is for pure curiosity, could it be possible to read
directly the mantissa and the power (see David's article if it sounds
like a foreign language) and to compare them for our 2 numbers? ... 1)
look a the power, if they have any difference, the two values can not be
equal. Then look at the mantissa and asses if the digit values are the
same or not...

Jean

David Fanning wrote:
> 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

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[Message index]

		Comparing 2 arrays By: teich on Sat, 25 August 2007 21:18
		Re: Comparing 2 arrays By: ph le sager on Wed, 29 August 2007 10:32
		Re: Comparing 2 arrays By: David Fanning on Wed, 29 August 2007 06:17
		Re: Comparing 2 arrays By: Carsten Lechte on Wed, 29 August 2007 03:31
		Re: Comparing 2 arrays By: Allan Whiteford on Wed, 29 August 2007 01:04
		Re: Comparing 2 arrays By: James Kuyper on Tue, 28 August 2007 13:02
		Re: Comparing 2 arrays By: Jean H. on Tue, 28 August 2007 12:18
		Re: Comparing 2 arrays By: Paul Van Delst[1] on Tue, 28 August 2007 12:33
		Re: Comparing 2 arrays By: David Fanning on Tue, 28 August 2007 11:56
		Re: Comparing 2 arrays By: Paul Van Delst[1] on Tue, 28 August 2007 11:43
		Re: Comparing 2 arrays By: David Fanning on Tue, 28 August 2007 09:52
		Re: Comparing 2 arrays By: Jean H. on Tue, 28 August 2007 09:20
		Re: Comparing 2 arrays By: David Fanning on Tue, 28 August 2007 09:18
		Re: Comparing 2 arrays By: Allan Whiteford on Tue, 28 August 2007 09:10

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