MarcumQ function

*To*: mathgroup at smc.vnet.net*Subject*: [mg130688] MarcumQ function*From*: Donagh Horgan <donagh.horgan at gmail.com>*Date*: Wed, 1 May 2013 21:43:31 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-outx@smc.vnet.net*Delivered-to*: mathgroup-newsendx@smc.vnet.net

Hello, I recently upgraded to Mathematica 9, and I've noticed a problem with the MarcumQ function. The following command should illustrate it: Plot[{MarcumQ[100, 10, x], 1 - MarcumQ[100, 10, 0, x]}, {x, 0, 30}] While the two functions are mathematically equivalent, the second incorrectly evaluates to zero between (approximately) x = 14 and x = 17. The problem only seems to occur when the first parameter is large. For example, the command Plot[{MarcumQ[50, 10, x], 1 - MarcumQ[50, 10, 0, x]}, {x, 0, 30}] evaluates correctly, while the command Plot[{MarcumQ[51, 10, x], 1 - MarcumQ[51, 10, 0, x]}, {x, 0, 30}] does not. I've tried wrapping the functions with the N command, e.g. N[f, 100], but the same problem occurs. I've also tried increasing $MaxExtraPrecision and $WorkingPrecision using Block, but with no luck. I've been testing my old code since I upgraded from Mathematica 8 a few days ago, so the error appears (to me, at least) to be new. All suggestions greatly appreciated! Best regards, Donagh Horgan

**Follow-Ups**:**Re: MarcumQ function***From:*Bob Hanlon <hanlonr357@gmail.com>