Problem with LegendreQ

*To*: mathgroup at smc.vnet.net*Subject*: [mg67548] Problem with LegendreQ*From*: mmandelberg at comcast.net*Date*: Fri, 30 Jun 2006 04:14:59 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

I seem to be getting incorrect numerical results for the LegendreQ[n,x] function. For example I get: LegendreQ[-1/2,5]//N = 1.00108 -1.17142 i so that the imaginary part is not zero. However, using the identity (Abramowitz and Stegun 8.3.13): LegendreQ[-1/2, x] = Sqrt[2/(x+1)] * EllipticK[Sqrt[2/(x+1)]] The answer should be: Sqrt[2/(5+1)]EllipticK[Sqrt[2/(5+1)]]//N 1.11187 Michael Mandelberg