[R] BUG: atan(1i) / 5 = NaN+Infi ?

[Leo Mada]

Dear Bert,

These behave like real divisions/multiplications:
complex(re=Inf, im = Inf) * 5
# Inf+Infi
complex(re=-Inf, im = Inf) * 5
# -Inf+Infi

The real division / multiplication should be faster and also is well behaved. I was expecting R to do the real division/multiplication on a complex number. Which R actually does for these very particular cases; but not when only Im(x) is Inf.

Sincerely,

Leonard

________________________________
From: Bert Gunter <bgunter.4567 using gmail.com>
Sent: Friday, September 6, 2024 1:12 AM
To: Duncan Murdoch <murdoch.duncan using gmail.com>
Cc: Leo Mada <leo.mada using syonic.eu>; r-help using r-project.org <r-help using r-project.org>
Subject: Re: [R] BUG: atan(1i) / 5 = NaN+Infi ?

Perhaps

> Inf*1i
[1] NaN+Infi

clarifies why it is *not* a bug.
(Boy, did that jog some long dusty math memories :-)  )

-- Bert

On Thu, Sep 5, 2024 at 2:48 PM Duncan Murdoch <murdoch.duncan using gmail.com<mailto:murdoch.duncan using gmail.com>> wrote:
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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