An embedded and charset-unspecified text was scrubbed... Name: not available URL: <https://stat.ethz.ch/pipermail/r-help/attachments/20110417/823eb407/attachment.pl>
cube root
6 messages · Branimir K. Hackenberger, Niels Richard Hansen, Berend Hasselman +3 more
?Syntax for precedence of operators.
On 16/04/11 22.51, Branimir K. Hackenberger wrote:
This is some interesting:
-8^(1/3)
[1] -2
x=(-8:8)
y=x^(1/3)
y
[1] NaN NaN NaN NaN NaN NaN NaN NaN 0.000000 1.000000 [11] 1.259921 1.442250 1.587401 1.709976 1.817121 1.912931 2.000000 So, can anybody explain this?! (Why is x[1]^(1/3)=y[1]=NaN, but -8^(1/3)=-2?) Thx!!! [[alternative HTML version deleted]]
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Niels Richard Hansen Web: www.math.ku.dk/~richard Associate Professor Email: Niels.R.Hansen at math.ku.dk Department of Mathematical Sciences nielsrichardhansen at gmail.com University of Copenhagen Skype: nielsrichardhansen.dk Universitetsparken 5 Phone: +1 510 502 8161 2100 Copenhagen ? Denmark
Branimir K. Hackenberger wrote:
This is some interesting:
-8^(1/3)
[1] -2
x=(-8:8)
y=x^(1/3)
y
[1] NaN NaN NaN NaN NaN NaN NaN NaN 0.000000 1.000000 [11] 1.259921 1.442250 1.587401 1.709976 1.817121 1.912931 2.000000 So, can anybody explain this?! (Why is x[1]^(1/3)=y[1]=NaN, but -8^(1/3)=-2?)
Operator precedence. See R FAQ 7.33 Why are powers of negative numbers wrong? Berend -- View this message in context: http://r.789695.n4.nabble.com/cube-root-tp3455020p3455027.html Sent from the R help mailing list archive at Nabble.com.
Hey :) In addition, although (-2)^3 = -8, (-8)^(1/3) != -2, mathematically. A fractional power of a negative number is complex. And this can be obtained properly in R:
(-8+0i)^(1/3)
[1] 1+1.732051i Cheers, Tsjerk
This is some interesting:
-8^(1/3)
[1] -2
x=(-8:8)
y=x^(1/3)
y
?[1] ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN NaN 0.000000 1.000000 [11] 1.259921 1.442250 1.587401 1.709976 1.817121 1.912931 2.000000 So, can anybody explain this?! (Why is x[1]^(1/3)=y[1]=NaN, but -8^(1/3)=-2?)
Operator precedence. See R FAQ 7.33 Why are powers of negative numbers wrong? Berend -- View this message in context: http://r.789695.n4.nabble.com/cube-root-tp3455020p3455027.html Sent from the R help mailing list archive at Nabble.com.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Tsjerk A. Wassenaar, Ph.D. post-doctoral researcher Molecular Dynamics Group * Groningen Institute for Biomolecular Research and Biotechnology * Zernike Institute for Advanced Materials University of Groningen The Netherlands
Hey :) In addition, although (-2)^3 = -8, (-8)^(1/3) != -2, mathematically. A fractional power of a negative number is complex. _Not_ in addition. The citation of FAQ 7.33 did not address the correct issue since the sequence was enclosed in parens. Yours is the only correct answer. For further discussion about various approaches to fractional powers of negative numbers one can get further approaches by searching the archives.
David. And this can be obtained properly in R: > (-8+0i)^(1/3) [1] 1+1.732051i Cheers, Tsjerk >> This is some interesting: >> >>> -8^(1/3) >> >> [1] -2 >> >>> x=(-8:8) >> >>> y=x^(1/3) >> >>> y >> >> ?[1] ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN >> NaN >> 0.000000 1.000000 >> >> [11] 1.259921 1.442250 1.587401 1.709976 1.817121 1.912931 2.000000 >> So, can anybody explain this?! (Why is x[1]^(1/3)=y[1]=NaN, but >> -8^(1/3)=-2?) >> > > Operator precedence. > > See R FAQ 7.33 Why are powers of negative numbers wrong? > > > Berend > Tsjerk Wassenaar wrote: > > Hey :) > > In addition, although (-2)^3 = -8, (-8)^(1/3) != -2, mathematically. A > fractional power of a negative number is complex. And this can be > obtained properly in R: > >> (-8+0i)^(1/3) > [1] 1+1.732051i > > Cheers, > > Tsjerk > >>> This is some interesting: >>> >>>> -8^(1/3) >>> >>> [1] -2 >>> >>>> x=(-8:8) >>> >>>> y=x^(1/3) >>> >>>> y >>> >>> ?[1] ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN >>> NaN >>> 0.000000 1.000000 >>> >>> [11] 1.259921 1.442250 1.587401 1.709976 1.817121 1.912931 2.000000 >>> So, can anybody explain this?! (Why is x[1]^(1/3)=y[1]=NaN, but >>> -8^(1/3)=-2?) >>> >> >> Operator precedence. >> >> See R FAQ 7.33 Why are powers of negative numbers wrong? >> >> >> Berend >> >> >> -- >> View this message in context: >> http://r.789695.n4.nabble.com/cube-root-tp3455020p3455027.html >> Sent from the R help mailing list archive at Nabble.com. >> >> ______________________________________________ >> R-help at r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > > > -- > Tsjerk A. Wassenaar, Ph.D. > > post-doctoral researcher > Molecular Dynamics Group > * Groningen Institute for Biomolecular Research and Biotechnology > * Zernike Institute for Advanced Materials > University of Groningen > The Netherlands > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > Tsjerk Wassenaar wrote: > > Hey :) > > In addition, although (-2)^3 = -8, (-8)^(1/3) != -2, mathematically. A > fractional power of a negative number is complex. And this can be > obtained properly in R: > >> (-8+0i)^(1/3) > [1] 1+1.732051i > > Cheers, > > Tsjerk > >>> This is some interesting: >>> >>>> -8^(1/3) >>> >>> [1] -2 >>> >>>> x=(-8:8) >>> >>>> y=x^(1/3) >>> >>>> y >>> >>> ?[1] ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN ? ? ?NaN >>> NaN >>> 0.000000 1.000000 >>> >>> [11] 1.259921 1.442250 1.587401 1.709976 1.817121 1.912931 2.000000 >>> So, can anybody explain this?! (Why is x[1]^(1/3)=y[1]=NaN, but >>> -8^(1/3)=-2?) >>> >> >> Operator precedence. >> >> See R FAQ 7.33 Why are powers of negative numbers wrong? >> >> >> Berend >> >> >> -- >> View this message in context: >> http://r.789695.n4.nabble.com/cube-root-tp3455020p3455027.html >> Sent from the R help mailing list archive at Nabble.com. >> >> ______________________________________________ >> R-help at r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > > > -- > Tsjerk A. Wassenaar, Ph.D. > > post-doctoral researcher > Molecular Dynamics Group > * Groningen Institute for Biomolecular Research and Biotechnology > * Zernike Institute for Advanced Materials > University of Groningen > The Netherlands > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- View this message in context: http://r.789695.n4.nabble.com/cube-root-tp3455020p3455118.html Sent from the R help mailing list archive at Nabble.com.
On 11-04-17 07:51, Branimir K. Hackenberger wrote:
This is some interesting:
-8^(1/3)
[1] -2
x=(-8:8)
y=x^(1/3)
y
[1] NaN NaN NaN NaN NaN NaN NaN NaN 0.000000 1.000000 [11] 1.259921 1.442250 1.587401 1.709976 1.817121 1.912931 2.000000 So, can anybody explain this?! (Why is x[1]^(1/3)=y[1]=NaN, but -8^(1/3)=-2?)
-8^(1/3) == (-8)^(1/3) # NA -8^(1/3) == -(8^(1/3)) # TRUE
Thx!!!
You're welcome.
Sascha Vieweg, saschaview at gmail.com