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MathGroup Archive 2000

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Re: assumptions question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg21912] Re: assumptions question
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 4 Feb 2000 02:54:42 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <87b0rh$o6c@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

it may help you to place the Assumptions options *behind* the
integration
range

Integrate[ Sin[k r]/(k r) * Exp[-I*(h k)^2 t /(2 m h)],
   {k, 0, Infinity},                 
   Assumptions-> {Sign[m] > 0, Sign[t h] > 0}]

Hope that helps
  Jens

Peter Jay Salzman wrote:
> 
> Dear all,
> 
> I have an integral whose output contains things which look like:
> 
>         (Sign[m] - I Sign[h t])
> 
> Since m is mass, h is hbar and t > 0, I placed placed a:
> 
>         Assumptions -> {Sign[m] > 0, Sign[t h] > 0}
> 
> inside the Integrate[ ] command.
> 
>         Integrate[ Sin[k r]/(k r) * Exp[-I*(h k)^2 t /(2 m h)],
>                 Assumptions-> {Sign[m] > 0, Sign[t h] > 0},
>                         {k, 0, Infinity}]
> 
> It seems to be ignoring me.  The Sign[m]'s keep showing up.  Is there a way
> to tell Mathematica that m is always positive?  I *thought* this was the way of
> doing it...
> 
> pete


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