Re: newbie problem with NIntegrate

• To: mathgroup at smc.vnet.net
• Subject: [mg49811] Re: newbie problem with NIntegrate
• From: Paul Abbott <paul at physics.uwa.edu.au>
• Date: Sun, 1 Aug 2004 18:48:43 -0400 (EDT)
• Organization: The University of Western Australia
• References: <cei8o5\$2he\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```In article <cei8o5\$2he\$1 at smc.vnet.net>,
"Xiaoxun" <dbjunxiao at hotmail.com> wrote:

>
> Geom = (200 >=x>= 100 && 50 >= y >= -50 && -20 <= z <= 20);
> gr[x_, y_, z_] := 2 /; Geom;
> gr[x_, y_, z_] := 0 /; ! (Geom);
> N[Integrate[gr[x, y, z], {x, 0, 300}, {y, -100, 100}, {z, -30, 30}]
> This gives a result of 799995.
> However, if changing the x range to {x,0,600} results 799993.
>                                 and {x,0,900} results 0;
>
> So what could we do to ensure the right answer?

<< Calculus`Integration`

and us Boole:

Integrate[2 Boole[200 >=x>= 100 && 50 >= y >= -50 && -20 <= z <= 20],
{x, 0, 300}, {y, -100, 100},   {z, -30, 30}]

800000

The answer does not change when the upper limit of x changes.

Cheers,
Paul

--
Paul Abbott                                   Phone: +61 8 9380 2734
School of Physics, M013                         Fax: +61 8 9380 1014
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```

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