Re: Is -1^(2/5) really undefined in R?
- To: mathgroup at smc.vnet.net
- Subject: [mg69136] Re: Is -1^(2/5) really undefined in R?
- From: dh <dh at metrohm.ch>
- Date: Wed, 30 Aug 2006 06:36:19 -0400 (EDT)
- References: <email@example.com>
- Sender: owner-wri-mathgroup at wolfram.com
version= Mathematica 5.1, Windows Hi Ben, There are actually five values of -1^(2/5), one of which is real. Consider -1=Exp[I (Pi + 2 n Pi)]. Then -1^(2/5)=Exp[2/5 I(I Pi + 2 n Pi)] Well, which value will mathematica return. You can find the answer in the manual under Power: "Power gives the principal value of a Exp[y Log[x]]", this is unfortunately not 1 as you expected, but on of the complex values. Daniel Ben wrote: > Is -1^(2/5) really undefined in R? > > Mathematica seems to think so, I guess since it looks like a negative square root, but > > -1^(2/5) = (-1^2)^(1/5) = 1^(1/5) = 1 > > Is this correct mathematically? > > cheers, > > BC >