[R] Trig functions strange results

[jim holtman]

FAQ 7.31

This is what happens with floating point number and you are only
printing out 7 digits of precision; look at the results
> cos(-1.570796)
[1] 0.0000003267949
> cos(-1.5707961)  # just incrementing the digit that was not displayed
[1] 0.0000002267949
> cos(-1.5707962)
[1] 0.0000001267949
> cos(-1.5707963)
[1] 0.00000002679490
> cos(-1.5707964) # notice the sign change
[1] -0.0000000732051
>


On Tue, Jul 14, 2009 at 1:45 PM, Nair, Murlidharan T<mnair at iusb.edu> wrote:
> I am trying to calculate coordinate transformations and in the process of debugging my code using debug I found the following
>
> Browse[1]> direction[i]
> [1] -1.570796
> Browse[1]> cos(direction[i])
> [1] 6.123032e-17
> Browse[1]> cos(-1.570796)
> [1] 3.267949e-07
> Browse[1]> direction[i]
> [1] -1.570796
> Browse[1]> cos(direction[i])
> [1] 6.123032e-17
> Browse[1]> cos(-1.570796)
> [1] 3.267949e-07
> Browse[1]> x<-direction[i]
> Browse[1]> x
> [1] -1.570796
> Browse[1]> cos(x)
> [1] 6.123032e-17
>
> I am not sure why I am getting one values when I am using a variable that stores the value and another when I use the value directly.  Am I missing something here?
>
> Can someone comment?
>
> Thanks ../Murli
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?