[Rd] Floating point precision / guard digits? (PR#13771)

From: <rbugs09_at_kreil.org>
Date: Fri, 19 Jun 2009 13:35:11 +0200 (CEST)


Full_Name: D Kreil
Version: 2.8.1 and 2.9.0
OS: Debian Linux
Submission from: (NULL) (141.244.140.179)

Group: Accuracy

I understand that most floating point numbers are approximated due to their binary storage. On the other hand, I thought that modern math CPUs used guard digits to protect against trivial underflows. Not true?

# integers, no problem
> 1+1+1==3
[1] TRUE
# binary floating point approximation underflows
> .1+.1+.1==.3

[1] FALSE
> .1+.1+.1==.3

[1] FALSE

# binary floating point exact for certain numbers
> .1+.1==.2

[1] TRUE I know that safe code should not test for quality of floats. Still, is R underutilizing the power of the underlying hardware?

Grateful for comments,
David.



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