From: Thomas Lumley <tlumley_at_u.washington.edu>

Date: Tue 20 Jun 2006 - 04:21:29 EST

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jun 20 04:25:42 2006

Date: Tue 20 Jun 2006 - 04:21:29 EST

On Mon, 19 Jun 2006, Hans-Peter wrote:

*> Hi,
**>
*

> I execute the following code snippet.What I don't understand is, that in the

*> first two cases the numbers shown don't correnspondant to the input (though
**> I have set the options to show 22 digits). When I assign the third number
**> which has one place, the display of the numbers is suddenly correct.
**>
**> Can anybody explain what happens here?
*

The problem is that you have set the options to show 22 digits, but the
numbers are stored to fewer than 16 digits

*> .Machine$double.eps
*

[1] 2.220446049250313080847e-16

Everything displayed after the 16th digit is effectively random (the actual values probably depend on exactly when the numbers are loaded into the 80-bit floating point registers on the CPU).

The actual results will vary from system to system (on my Linux system the output of x is the same at all stages, and is different from what you report), but nothing beyond the sixteenth digit is at all meaningful.

-thomas

> (this is just a sample, my real problem lies in numbers that I import from a

*> datafile and I don't know how to control them when this switching occurs)
**>
**> ###########################
**> options( digits=22 )
**> x <- matrix(NA, 3,1)
**> x[1] <- 6.94788635771657950
**> x # 6.947886357716580 # DIFFERENT ???
**> # NA
**> # NA
**> x[1] == 6.94788635771657950 # but is the same
**>
**> x[2] <- 8.34284937565404050
**> x # 6.947886357716580 # DIFFERENT ???
**> # 8.342849375654041 # DIFFERENT ???
**> # NA
**> x[1] == 6.94788635771657950 # but is the same
**>
**> x[3] <- 0.19043842368566377
**> x # 6.94788635771657950 # NOW OK!!!
**> # 8.34284937565404050 # " "
**> # 0.19043842368566377 # " "
**> x[1] == 6.94788635771657950 # but is the same
**>
**>
**> ###
**> platform i386-pc-mingw32
**> arch i386
**> os mingw32
**> system i386, mingw32
**> status
**> major 2
**> minor 3.1
**> year 2006
**> month 06
**> day 01
**> svn rev 38247
**> language R
**> version.string Version 2.3.1 (2006-06-01)
**>
**>
**> --
**> Regards,
**> Hans-Peter
**>
**> [[alternative HTML version deleted]]
**>
**> ______________________________________________
**> R-help@stat.math.ethz.ch mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-help
**> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
**>
*

Thomas Lumley Assoc. Professor, Biostatistics tlumley@u.washington.edu University of Washington, Seattle ______________________________________________R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jun 20 04:25:42 2006

Archive maintained by Robert King, hosted by
the discipline of
statistics at the
University of Newcastle,
Australia.

Archive generated by hypermail 2.1.8, at Tue 20 Jun 2006 - 06:12:17 EST.

*
Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help.
Please read the posting
guide before posting to the list.
*