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Re: Dificulty on Integrate function!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96972] Re: [mg96934] Dificulty on Integrate function!
  • From: DrMajorBob <btreat1 at austin.rr.com>
  • Date: Sat, 28 Feb 2009 06:44:24 -0500 (EST)
  • References: <200902271116.GAA21652@smc.vnet.net>
  • Reply-to: drmajorbob at bigfoot.com

Sorry, I meant d in the denominator (not t), and integrating d (not t) on  
an interval starting with 0.

Bobby

On Sat, 28 Feb 2009 00:42:52 -0600, DrMajorBob <btreat1 at austin.rr.com>  
wrote:

> You want to integrate an equation (but equations CAN'T be integrated)  
> and anyway, you haven't given us an equation. (Just an expression.)
>
> Indefinite integration of that expression w.r.t. b, c, and d would still  
> give a function of FIVE variables -- not just t and a.
>
> And definite integration w.r.t. b, c, and d probably isn't possible,  
> either -- I'm pretty sure there's no closed form expression for it, when  
> t and a are undefined (variable).
>
> So you'll have to rein in your wants, here. What CAN be done (maybe) is  
> something like
>
> f[t_, a_][b_, c_,
>     d_] = (5.985857026794833*^-14*(14 + c)^2.37*
>       E^(-0.0003630681026445808*(-50.29 + b)^2 - c/41 -
>          0.0003125*(-43.7 + d)^2 - b/d + t/d -
>          1.1985780806058064*^-6*(-3535.42 +
>              c + ((a - c)*E^((-b + t)/d))/(t/b)^(b/d))^2))/(t/b)^(b/
>        d);
> g[t_?NumericQ, a_?NumericQ] :=
>   NIntegrate[f[t, a][b, c, d], {b, 0, 170.}, {c, 0, 400.}, {d, 0, 170.}]
>
> g[0.5, 0.3]
>
> But, if you execute that, you'll see that NIntegrate has convergence  
> problems.
>
> Experiment with various options to NIntegrate and maybe, for some values  
> of t and a, you can get convergence.
>
> Your expression has t in a couple of denominators, but you want to  
> integrate with t from 0 to (doesn't matter what). That in itself may  
> make convergence impossible. So changing the lower limit might help a  
> lot.
>
> Bobby
>
> On Fri, 27 Feb 2009 05:16:04 -0600, <negedea at googlemail.com> wrote:
>
>> Dear all,
>>
>> I got a problem in integrating the expression (given below in input
>> form) on Mathematica. Please give me some hints or a way around to get
>> the solutions. . I want to integrate the equation  with respect to b,
>> c, and d. So that I get an equation only in terms of t and a. I tried
>> to use Integrate function in Mathematica both in the form of definite
>> and indefinite integral but it could not turn out the result. If the
>> indefinite integral is not working the ranges of integration for
>> definite integral shall be the following {b, 0, 170}, {c, 0, 400} and
>> {d, 0,170}.
>>
>> (5.985857026794833*^-14*(14 + c)^2.37*E^(-0.0003630681026445808*
>> (-50.29 + b)^2 - c/41 - 0.0003125*(-43.7 + d)^2 - b/d + t/d -
>> 1.1985780806058064*^-6*(-3535.42 + c + ((a - c)*E^((-b + t)/d))/(t/b)^
>> (b/d))^2))/(t/b)^(b/d)
>>
>> Please please help me. If I could not get this solution I have to
>> discard so many things I spent considerable time on!
>>
>> Thanking you in advance.
>>
>> Negede
>>
>
>
>



-- 
DrMajorBob at bigfoot.com


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