From: Ted Harding <Ted.Harding_at_nessie.mcc.ac.uk>

Date: Tue 29 Mar 2005 - 21:59:28 EST

E-Mail: (Ted Harding) <Ted.Harding@nessie.mcc.ac.uk> Fax-to-email: +44 (0)870 094 0861

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 Mar 29 21:16:16 2005

Date: Tue 29 Mar 2005 - 21:59:28 EST

On 29-Mar-05 Klaus-Peter Pleissner wrote:

> Hi all,

*> I have to calculate an expression using acos -function.
**> A strange result of acos appears
**>
**> *1. case with error*
**>
**> ss <- sin(10.74*pi/180)**2
**> +(cos(10.74*pi/180)*cos(10.74*pi/180)*cos(0*pi/180))
**> ss
**> acos(ss)
**>
**> [1] NaN
**> Warning message:
**> NaNs produced in: acos(ss)
**>
**> *2. case without error*
**>
**> ss <- sin(10.7*pi/180)**2
**> +(cos(10.7*pi/180)*cos(10.7*pi/180)*cos(0*pi/180))
**> ss
**> acos(ss)
**>
**> In both cases the variable ss equals 1. I think there
**> is a problem with precision. If I multiply ss by
**> 0.999999999 (ss*0.99999999) no error occurs. How the
**> results can be explained ?
*

The explanation is:

sin(10.74*pi/180)**2

+(cos(10.74*pi/180)*cos(10.74*pi/180)

*cos(0*pi/180))

-1

Best wishes,

Ted.

E-Mail: (Ted Harding) <Ted.Harding@nessie.mcc.ac.uk> Fax-to-email: +44 (0)870 094 0861

Date: 29-Mar-05 Time: 11:59:28 ------------------------------ XFMail ------------------------------ ______________________________________________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 Mar 29 21:16:16 2005

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