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Re: machine precision [message #66505 is a reply to message #66504]

Mon, 18 May 2009 06:04

Wout De Nolf
Messages: 194
Registered: October 2008

Senior Member

On Mon, 18 May 2009 05:53:36 -0600, David Fanning <news@dfanning.com>
wrote:

> Uh, Wox, I think you need to read this article again:
>
> http://www.dfanning.com/math_tips/sky_is_falling.html

Ow boy, sorry for bringing this up again, but in the last example
given in your famous article, why is:

f=470.0 - (4.70*100)
d=470d - (4.70d*100)
print,'Bigger than precision:',f,(machar()).eps
print,'Smaller than precision:',d,(machar(/double)).eps

I understand that when you give 4.7 to a computer, it stores a number
close to it. When given 4.70d, the same thing happens, only now we're
closer than with single-precision. Why is the machine precision (EPS
from machar) not reflecting this?

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[Message index]

		Re: machine precision By: Wout De Nolf on Wed, 20 May 2009 06:08
		Re: machine precision By: Carsten Lechte on Wed, 20 May 2009 03:44
		Re: machine precision By: jameskuyper on Wed, 20 May 2009 03:28
		Re: machine precision By: Carsten Lechte on Wed, 20 May 2009 01:46
		Re: machine precision By: David Fanning on Tue, 19 May 2009 20:01
		Re: machine precision By: jameskuyper on Tue, 19 May 2009 18:41
		Re: machine precision By: Kenneth P. Bowman on Tue, 19 May 2009 11:15
		Re: machine precision By: jeffnettles4870 on Tue, 19 May 2009 08:16
		Re: machine precision By: jameskuyper on Mon, 18 May 2009 18:44
		Re: machine precision By: Wout De Nolf on Mon, 18 May 2009 07:02
		Re: machine precision By: Wout De Nolf on Mon, 18 May 2009 06:55
		Re: machine precision By: jameskuyper on Mon, 18 May 2009 06:33
		Re: machine precision By: David Fanning on Mon, 18 May 2009 06:30
		Re: machine precision By: Wout De Nolf on Mon, 18 May 2009 06:04
		Re: machine precision By: David Fanning on Mon, 18 May 2009 04:53

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