From: Petr Savicky <savicky_at_cs.cas.cz>

Date: Wed, 11 Nov 2009 13:29:50 +0100

R-devel_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-devel Received on Wed 11 Nov 2009 - 12:35:11 GMT

Date: Wed, 11 Nov 2009 13:29:50 +0100

> # Hi there.

*> # I'm not sure whether or not this is a bug.
*

No, this is not a bug. See FAQ 7.31 at

http://cran.r-project.org/doc/FAQ/R-FAQ.html
and the comments below.

> # But it surely is an unexpected behaviour.

*>
**> V <- seq(from=0,to=1,by=0.1)
**>
**> # Should generate a sequence with a step of 0.1
**>
**> V==0
**> # [1] TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
**> # Ok!
**>
**> V==0.1
**> # [1] FALSE TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
**> # Ok!
**>
**> V==0.6
**> # [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
**> # None?
**>
**> V[7]
**> # [1] 0.6
**> V[7]==0.6
**> # [1] FALSE
**> # Rounding!?
*

Yes. The sequence of operations, which leads to V[7], produce
slightly different rounding error than the direct conversion of 0.6
to binary representation. So, we have

formatC(V[7], digits=20) # [1] "0.60000000000000008882"
formatC(0.6, digits=20) # [1] "0.5999999999999999778"

See

http://wiki.r-project.org/rwiki/doku.php?id=misc:r_accuracy
for more examples and explanations.

Petr Savicky.

*> V[8]
*

> # [1] 0.7

*> V[8]==0.7
**> # [1] FALSE
**> # Rounding!?
**>
**> V[9]
**> # [1] 0.8
**> V[9]==0.8
**> # [1] TRUE
**> # Back to normal
**>
**> # The generated sequence is fine for all values except for 0.6
**> # and 0.7, which appear to be somewhat off the expected value.
**>
**> # According to the R manual the sequence is generated in the form:
**> # from, from+by, ..., to
**> # which is not the case.
**>
**> # Either the function or the documentation lead to an unexpected
**> # behaviour of seq(from,to,by).
**>
**> # Thanks!
**>
**> ______________________________________________
**> R-devel_at_r-project.org mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-devel
**>
*

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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Wed 11 Nov 2009 - 12:35:11 GMT

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