On Wed, 31 Mar 2010, William Dunlap wrote:
I'm having trouble grokking complex NaN's.
This first set examples using complex(re=NaN,im=NaN)
give what I expect
> Re(complex(re=NaN, im=NaN))
[1] NaN
> Im(complex(re=NaN, im=NaN))
[1] NaN
> Arg(complex(re=NaN, im=NaN))
[1] NaN
> Mod(complex(re=NaN, im=NaN))
[1] NaN
> abs(complex(re=NaN, im=NaN))
[1] NaN
and so do the following
> Re(complex(re=1, im=NaN))
[1] 1
> Im(complex(re=1, im=NaN))
[1] NaN
> Re(complex(re=NaN, im=1))
[1] NaN
> Im(complex(re=NaN, im=1))
[1] 1
but I don't have a good mental model that explains
why the following produce NA instead of NaN.
Just a guess here:
as.complex(sqrt(as.complex(-1)))
[1] 0+1i
as.complex(sqrt(-1))
[1] NA
Warning message:
In sqrt(-1) : NaNs produced
It protects from assuming that the latter truly is not a number.
Chuck
> as.complex(NaN)
[1] NA
> Im(complex(modulus=NaN, argument=NaN))
[1] NA
> Re(complex(modulus=NaN, argument=NaN))
[1] NA
> Re(1i * NaN)
[1] NA
> Im(1i * NaN)
[1] NA
> Re(NaN + 1i)
[1] NA
> Im(NaN + 1i)
[1] NA
It may be that if as.complex(NaN), and its C equivalent,
were changed to return complex(re=NaN,im=NaN) then the
arithmetic examples would return NaN. Is there a
better way for me to model how NaN's in complex numbers
should work or is this a bug?
While I was looking into this I noticed a bug in str():
> str(NA_complex_)
Error in FUN(X[[1L]], ...) : subscript out of bounds
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cbe...@tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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