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Re: Comparing 2 arrays [message #55540]

Mon, 27 August 2007 08:06

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Conor writes:

> Hmm... I think Jean might be on to something. After all, the error in
> question hear is the rounding error of the computer, and that rounding
> error is always an error on the last 'bit' of a floating point
> number. So for instance if you had two floating point numbers:
>
> 1.1123453e15
> and
> 1.1123454e15
>
> These might be the same number (to within the rounding error) but the
> difference between them is about 6.7e07. That's assuming of course
> that I'm properly understanding floating point representation (I'm an
> astronomer, not a computer engineer).

I guess I'm thinking more about how a number got INTO
the array in the first place. If it got there as a result
of some kind of calculation, accumulative rounding errors
could be a great deal larger than machine precision. And
yet, you might still want these numbers to be "equal" for
analysis purposes.

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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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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