Re: double integral
- To: mathgroup at smc.vnet.net
- Subject: [mg34201] Re: double integral
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Thu, 9 May 2002 05:16:04 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <abaenr$s00$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
Mathematica returns nonsense because you enter nonsens.
The correct order of integration is
Integrate[x^2, {x, y, 6/y}, {y, 0, Sqrt[6]}]
you have to integrate *first* over x and than over y
and not integrate over y and than over x with bounds
that depend on y.
Regards
Jens
Higinio Ramos wrote:
>
> Why does Integrate fail in solving the double integral?
> In[1]:=Integrate[x^2,{y,0,Sqrt[6]},{x,y,6/y}]
> Out[1]= -9
>
> Of course, If I do the evaluations in two steps, the result is
> correct:(the integral does not converge)
> In[3]:=
> 2 6
> Integrate[x , {x, y, -}]
> y
> Out[3]=
> 3
> 72 y
> -- - --
> 3 3
> y
>
> In[4]:=
> 3
> 72 y
> Integrate[-- - --, {y, 0, Sqrt[6]}]
> 3 3
> y
> \!\(Integrate::"idiv" : "Integral of \!\(72\/y\^3 - y\^3\/3\) does not
> converge on \!\({0, \\@6}\)."\)
> Out[4]=
> 3
> 72 y
> Integrate[-- - --, {y, 0, Sqrt[6]}]
> 3 3
> y