[R] R-1.7.1 regression test failure on alphaev68-dec-osf5.1

[Peter Dalgaard BSA]

"Jeff Lewis" <jlewis at genomecorp.com> writes:

> > Well, it seems to be an accuracy issue, so the first question would be
> > what the values on both sides of the equality are (just start up R and
> > enter the expressions on te command line). You might have
> > 
> > 1) Completely wrong results in complex arithmetic 
> > 2) Slightly less than optimal accuracy
> > 3) An underestimated .Machine$double.eps
> > 
> > Case 2) seems most likely, but case 3) has been observed with buggy
> > compilers that optimize calculations where they shouldn't.
> 
> 
> 
> Thanks for the quick response.  The two sides of the equality are
> definately different.  Here's what I'm seeing
> 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> > pi
> [1] 3.141593
> 
> > 1i
> [1] 0+1i
> 
> > pi*1i
> [1] 0+3.141593i
> 
> > exp(pi*1i)
> [1] -1+1.224647e-16i
> 
> > log(exp(pi*1i))
> [1] 0+3.141593i
> 
> > log(exp(pi*1i)) / 1i
> 
> [1] 3.141593+0i
> 
> > pi - log(exp(pi*1i)) / 1i
> [1] 4.440892e-16+0i
> 
> > Mod(pi - log(exp(pi*1i)) / 1i)
> [1] 4.440892e-16
> 
> > .Machine$double.eps
> [1] 2.220446e-16
> 
> > Mod(pi - log(exp(pi*1i)) / 1i) < .Machine$double.eps
> [1] FALSE
> 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> 
> I get the same thing from R 1.6.2, which I compiled about six months
> ago.  Is there anything I can/should do to fix this?

Not really. It seems that your platform just has slightly less
accurate complex log/exp routines than the most common ones (Linux and
Sparc/Solaris both give exact zero). Probably the check is simply
overly stringent.

You might want to change the check to say  ... < 3*.Machine$double.eps
or so and rerun, to check whether the rest of the checks pass.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907