[ruby-dev:42119] Re: Math::atan2(0, 0) on ruby 1.9.2

=1B$B$`$i$?$G$9!#=1B(B

On 2010/08/23, at 23:05, KUBO Takehiro wrote:

> =1B$B5WJ]$G$9!#=1B(B
>=20
> 2010/8/23 Yusuke ENDOH <[e-mail]>:
>> =1B$B1sF#$G$9!#=1B(B
>>=20
>> atan2 =1B$B$O6K:BI8JQ49$K;H$o$l$k$N$G!"=1B(B[hypot(x, y), atan2(x, =
y)] =1B$B$,=1B(B
>> x =3D y =3D 0 =1B$B$N;~$K%(%i!<$K$J$k$N$OITJX!"$H$$$&$h$&$J$3$H$,=1B(B =
FreeBSD
>> =1B$B$N=1B(B manpage =1B$B$K=3Dq$$$F$"$j$^$7$?!#=1B(B
>> =1B$B$3$N=1B(B rationale =1B$B$O8D?ME*$K$OG<F@$G$-$^$9!#=1B(B
>>=20
>> =1B$B$^$?!"$$$/$D$+=1B(B regression =
=1B$B$b0z$-5/$3$7$F$$$k$h$&$J$N$G!"=1B(Batan2 =1B$B$K=1B(B
>> =1B$B4X$7$F$O=1B(B SUSv3 =
=1B$B$K=3D>$C$F$*$/$H$h$$$N$G$O$J$$$G$7$g$&$+!#=1B(B
>=20
> =1B$B$$$C$=3D$N$3$H!"=1B(BJava =
=1B$B$N;EMM$r??;w$9$k$H$$$&$N$b$"$j$+$b$7$l$J$$!#=1B(B

=1B$B2?$N:,5r$b$J$/C;MmE*$K=1B(B Java =
=1B$B$K9g$o$;$h$&$H$$$&9M$($K$O;?F1$G$-$^$;$s$7!"=1B(B
=1B$B$J$<$=3D$3$G=1B(B Java =
*=1B$B$@$1=1B(B*=1B$B$,=3DP$F$/$k$N$+$bNI$/J,$+$j$^$;$s!#=1B(B

Math.atan2 =
=1B$B$O?t3X$N4X?t$G$9$+$i!"$G$-$k$@$1?t3XE*$K9M$($?$$$G$9$7!"=1B(B
=1B$BB>$N8@8l$r;29M$K$9$k$J$i=1B(B Java =
=1B$B0J30$N8@8l$b8+$?$[$&$,NI$$$G$7$g$&!#=1B(B


Common Lisp [1] =1B$B$H=1B(B Scheme (R6RS) [2] =
=1B$B$rD4$Y$F$_$k$H!"<!$N$h$&$K$J$C$F$$$^$9=1B(B:

Common Lisp =1B$B$N>l9g=1B(B
-------------------
 x   y  atan2(x, y)
-------------------
+0  +0  +0
+0  -0  -0
-0  +0  +pi
-0  -0  -pi
-------------------

Scheme =1B$B$N>l9g=1B(B (R6RS)
-------------------
 x   y  atan2(x, y)
-------------------
+0  +0  +0
+0  -0  -0
-0  +0  +pi
-0  -0  -pi
 0  +0  pi/2
 0  -0  -pi/2
-------------------

Common Lisp =1B$B$O=1B(B SUSv3 =1B$B$HF1$8$G!"=1B(BScheme =
=1B$B$O>l9gJ,$1$,=1B(B2=1B$B$DA}$($F$$$^$9!#=1B(B
Haskell =1B$B$N=1B(B atan2 =1B$B$O=1B(B Common Lisp =1B$B$HF1$8$G$7$?!#=1B=
(B

# =1B$B$A$J$_$K=1B(B Mathematica =1B$B$O!">e5-$NCM$O=1B(B indefinite =
=1B$B$H$7$FCM0h$,JV$C$F$-$^$9!#=1B(B


=1B$B$3$l$i$NCM$,$I$3$+$iMh$?$N$+$r9M$($k$H!"$I$&$b=1B(B

atan2(=1B$B!^=1B(B0, =1B$B!^=1B(B0) =3D lim_{x->=1B$B!^=1B(B0} =
lim_{y->=1B$B!^=1B(B0} atan2(x, y)  (=1B$BJ#9fF1=3Dg=1B(B)

=1B$B$3$N<0$+$iMh$F$$$k$h$&$G$9!#=1B(BWikipedia [3] =1B$B$K$"$k=1B(B =
atan2 =1B$B$N=1B(B3=1B$B<!85%0%i%U$r8+$l$P=1B(B
Scheme =1B$B$NDj5A$r:NMQ$9$k;v$,E,@Z$J$h$&$K46$8$^$9!#=1B(B


[1] =
http://www.lispworks.com/documentation/HyperSpec/Body/f_asin_.htm#atan
[2] =
http://practical-scheme.net/wiliki/wiliki2.cgi?R6RS:%E7%BF%BB%E8%A8%B3:R6R=
S:11.7.3.2%20Transcendental%20functions
[3] http://en.wikipedia.org/wiki/Atan2#Variations

--
Kenta Murata
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=1B$B!X=1B(BRuby =1B$B5U0z$-%l%7%T!Y=1B(B =
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