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MathGroup Archive 2005

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Re: problem with InverseLaplaceTransform

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58004] Re: [mg57985] problem with InverseLaplaceTransform
  • From: Selwyn Hollis <sh2.7183 at earthlink.net>
  • Date: Thu, 16 Jun 2005 05:36:06 -0400 (EDT)
  • References: <200506150958.FAA29790@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

I'm afraid that you're asking a bit too much of Mathematica. The  
transform you're trying to invert has an almost general cubic factor  
in its denominator. (Look at Simplify[ExpandDenominator 
[yourexpression]].) Even with specific instances of the seven  
parameters in it, Mathematica typically gives the inverse transform  
in terms of a slew of Root[] expressions (representing roots of cubic  
equations).

By the way, Mathematica probably isn't crashing on you; it's just  
working. You can (usually) stop it with Abort Evaluation in the  
Kernel menu.


Selwyn Hollis
http://www.appliedsymbols.com


On Jun 15, 2005, at 5:58 AM, Barry Shaw wrote:

>
> Hi,
>
>
>
> I'm pretty new to Mathematica and am having difficulty trying to  
> derive
> an inverse laplace transform using Mathematica.  When I run the code,
> Mathematica starts to run (says "running..."), but then just continues
> to remain like that and doesn't give an answer....as if it has crashed
> or something.  The code I`m trying to run is below (layout messed up,
> but if you copy and paste it back into Mathemtica it`s fine):
>
>
>
> InverseLaplaceTransform[{{(muone (mufour + s) (lambdathree + muthree +
>
>                   s) (lambdatwo + mutwo + s) +
>
>             lambdaone (lambdathree (lambdatwo mufour +
>
>                         mutwo (mufour + s)) + (mufour +
>
>                         s) (lambdatwo muthree +
>
>                         mutwo (muthree + s))))/(s (mufour + s)
> (lambdaone +
>
>                 muone + s) (lambdathree + muthree + s) (lambdatwo +
> mutwo +
>
>                 s) (1 - (muone (mufour + s) (lambdathree + muthree +
>
>                             s) (lambdatwo + mutwo + s) +
>
>                       lambdaone (lambdathree (lambdatwo mufour +
>
>                                   mutwo (mufour + s)) + (mufour +
>
>                                   s) (lambdatwo muthree +
>
>                                   mutwo (muthree + s))))/((mufour +
>
>                           s) (lambdaone + muone + s) (lambdathree +
> muthree +
>
>                           s) (lambdatwo + mutwo + s))))}}, s, t]
>
>
>
> Can anybody explain my problem?
>
>
>
> Thanks,
>
> Barry
>
>
>
>


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