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MathGroup Archive 2007

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Re: Integration variables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg78361] Re: [mg78307] Integration variables
  • From: "matteo manni" <m_manni_m at hotmail.com>
  • Date: Fri, 29 Jun 2007 05:43:37 -0400 (EDT)

I think that the problem was that I was triyn to integrate in cos[Ttheta], 
which is a funtion and not a variable, as it was underlined in the previous 
answer.
In the same post they suggested me to change

d Cos[Ttheta]

into

-sin[Ttheta]dTtheta

in order to have a valid integration variable. In this case I have to change 
the interval of integration from [-1,1] that I had before (referring to 
cos[Ttheta])
) to [0,Pi] (which is the equivalent for the Thata angle).


>From: DrMajorBob <drmajorbob at bigfoot.com>
>Reply-To: drmajorbob at bigfoot.com
>To: mattew <m_manni_m at hotmail.com>, mathgroup at smc.vnet.net
>Subject: Re: [mg78307] Integration variables
>Date: Thu, 28 Jun 2007 11:34:46 -0500
>
>You didn't post the code, so it's just a guess what you actually entered,  
>but...
>
>Rather than Integrate[f[x], g[x]], you must use Integrate[f[x] g'[x], x].
>
>Bobby
>
>On Thu, 28 Jun 2007 03:20:02 -0500, mattew <m_manni_m at hotmail.com> wrote:
>
>>Hi everybody, Mathematica gives us the possibility to use spherical  
>>coordinates (r,Ttheta,Pphi): I'm trying to write an integral in the  polar 
>>angle Ttheta of the form:
>>
>>Integral in [-1,1] Ttheta dCos(Ttheta)
>>
>>where Ttheta is the polar angle and the integration variable is the  
>>cosine of Ttheta in the interval [-1,1].
>>
>>I got the following error:
>>
>>ntegrate::ivar: "Cos[Ttheta] is not a valid variable."
>>
>>Does anyone knows the reason for that?
>>
>>p.s: It happens with any system of coordinates, actually.
>>
>>
>
>
>
>--
>DrMajorBob at bigfoot.com

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