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MathGroup Archive 2002

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Re: Integrate malfunction?

  • To: mathgroup at
  • Subject: [mg33872] Re: [mg33860] Integrate malfunction?
  • From: BobHanlon at
  • Date: Sun, 21 Apr 2002 06:12:18 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

In a message dated 4/20/02 4:28:27 AM, sbstory at writes:

>I recently had to do an integral which should evaluate to be a very very
>small quantity. The function is always positive, but the integral gives
>me a
>negative number. I think this is a malfunction of some sort. Here's the
>amu = 1.661*10^-27
>nitrogen = 28*amu
>k = 1.381*10^-23
>t = 1000
>  4 Pi ((nitrogen/(2 Pi k t))^(3/2)) x^2 Exp[(-1 nitrogen x^2)/(2 k t)],
>11000, Infinity}]
>Out[13]= -5.878291776559734*10^-16
>does anyone know why this is happening? i tried NIntegrate instead, but
>General::"unfl": "Underflow occurred in computation."

Use higher precision.  For example, you can use rational numbers


    {x, 11000, Infinity}]]]


Note that for maximum precision you want to use FullSimplify before 
converting to a numerical result.

Bob Hanlon
Chantilly, VA  USA

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