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Re: Comparing 2 arrays [message #55663 is a reply to message #55564]

Tue, 28 August 2007 09:52

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Jean H. writes:

> 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...

I just thought there should be some multiple to account
for possible accumulative round-off errors. Two was an
arbitrary selection, but based on something I read in the
previous discussion. Naturally, I decided on this after
I wrote the note describing it. :-)

> 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...

I don't think IDL has easy access to the numbers as they
are stored. I guess you could do it yourself, but I'm
pretty sure it involves "twos complement" arithmetic,
which I've never been sufficiently motivated to learn. :-(

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]

		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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