MathGroup Archive 2013

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: MarcumQ function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg130698] Re: MarcumQ function
  • From: Bob Hanlon <hanlonr357 at gmail.com>
  • Date: Fri, 3 May 2013 03:52:29 -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
  • References: <20130502014331.5FD146A86@smc.vnet.net>

It's a precision issue. Specify a working precision rather than using
machine precision; however, it slows down the computations.


Plot[{
  MarcumQ[100, 10, x],
  1 - MarcumQ[100, 10, 0, x]},
 {x, 0, 30},
 WorkingPrecision -> 20]


Plot[{
  MarcumQ[51, 10, x],
  1 - MarcumQ[51, 10, 0, x]},
 {x, 0, 30},
 WorkingPrecision -> 20]



Bob Hanlon




On Wed, May 1, 2013 at 9:43 PM, Donagh Horgan <donagh.horgan at gmail.com>wrote:

> 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
>
>




  • Prev by Date: Re: How to set Mathematica not return huge float numbers
  • Next by Date: Re: Formula Stirlinga
  • Previous by thread: MarcumQ function
  • Next by thread: Re: MarcumQ function