> x <- complex(imag = Inf) > x [1] 0+Infi > x*1 [1] NaN+Infi > x+0 [1] 0+Infi
R does the addition and subtraction "coordinatewise"; the C library handles everything else. This results in 2 different ways the point at infinity is printed. (Correction requested if this is wrong) Bert On Thu, Sep 5, 2024 at 4:07 PM Jeff Newmiller via R-help < r-help@r-project.org> wrote: > atan(1i) -> 0 + Inf i > complex(1/5) -> 0.2 + 0i > atan(1i) -> (0 + Inf i) * (0.2 + 0i) > -> 0*0.2 + 0*0i + Inf i * 0.2 + Inf i * 0i > infinity times zero is undefined > -> 0 + 0i + Inf i + NaN * i^2 > -> 0 + 0i + Inf i - NaN > -> NaN + Inf i > > I am not sure how complex arithmetic could arrive at another answer. > > I advise against messing with infinities... use atan2() if you don't > actually need complex arithmetic. > > On September 5, 2024 3:38:33 PM PDT, Bert Gunter <bgunter.4...@gmail.com> > wrote: > >> complex(real = 0, imaginary = Inf) > >[1] 0+Infi > > > >> Inf*1i > >[1] NaN+Infi > > > >>> complex(real = 0, imaginary = Inf)/5 > >[1] NaN+Infi > > > >See the Note in ?complex for the explanation, I think. Duncan can correct > >if I'm wrong. > > > >-- Bert > > > >On Thu, Sep 5, 2024 at 3:20 PM Leo Mada <leo.m...@syonic.eu> wrote: > > > >> 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.4...@gmail.com> > >> *Sent:* Friday, September 6, 2024 1:12 AM > >> *To:* Duncan Murdoch <murdoch.dun...@gmail.com> > >> *Cc:* 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 ? > >> > >> 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.dun...@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 > >> > >> ______________________________________________ > >> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >> https://stat.ethz.ch/mailman/listinfo/r-help > >> PLEASE do read the posting guide > >> https://www.R-project.org/posting-guide.html > >> and provide commented, minimal, self-contained, reproducible code. > >> > >> > > > > [[alternative HTML version deleted]] > > > >______________________________________________ > >R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > >https://stat.ethz.ch/mailman/listinfo/r-help > >PLEASE do read the posting guide > https://www.R-project.org/posting-guide.html > >and provide commented, minimal, self-contained, reproducible code. > > -- > Sent from my phone. Please excuse my brevity. > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > https://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide https://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
