On 2024-09-05 6:12 p.m., Leo Mada wrote:
Dear Duncan,
Here is also the missing information:
R version 4.4.1 (2024-06-14 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 10 x64 (build 19045)
Regarding the results:
atan(1i)
# 0+Infi
Re(atan(1i))
# 0
Im(atan(1i))
# Inf
0 + Inf i is a valid complex number:
tan(atan(1i))
# 0+1i
Inf / 5
# Inf
Note: atan(1i) / 5 should have generated 0 + Inf * 1i; even the explicit
complex number fails:
complex(re=0, im = Inf) / 5
# NaN+Infi
complex(re=Inf, im = Inf) / 5
# Inf+Infi
I presume that R tries to do the complex division, although the real
division is well defined.
I imagine that what happens is that when one operand is complex, both
are coerced to complex and the operation is carried out. I had assumed
this was documented in ?complex, but I don't see it there. Maybe it
should be.
If you want z/5 to be carried out using the correct mathematical
approach, you'll probably have to define it yourself. For example,
CxByReal <- function(num, denom) {
if (is.complex(denom)) stop("this is for a real denominator!")
complex(real = Re(num)/denom, imaginary = Im(num)/denom)
}
CxByReal(complex(real=0, imaginary=Inf), 5)
# [1] 0+Infi
Duncan Murdoch
Sincerely,
Leonard
------------------------------------------------------------------------
*From:* Duncan Murdoch <murdoch.dun...@gmail.com>
*Sent:* Friday, September 6, 2024 12:40 AM
*To:* Leo Mada <leo.m...@syonic.eu>; r-help@r-project.org
<r-help@r-project.org>
*Subject:* Re: [R] BUG: atan(1i) / 5 = NaN+Infi ?
On 2024-09-05 4:23 p.m., Leo Mada via R-help wrote:
Dear R Users,
Is this desired behaviour?
I presume it's a bug.
atan(1i)
# 0+Infi
tan(atan(1i))
# 0+1i
atan(1i) / 5
# NaN+Infi
There's no need to involve atan() and tan() in this:
> (0+Inf*1i)/5
[1] NaN+Infi
Why do you think this is a bug?
Duncan Murdoch
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