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MathGroup Archive 2007

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Re: Re: Problem with inverse laplace transform (FIX)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81201] Re: Re: Problem with inverse laplace transform (FIX)
  • From: "Alexey Nikitin" <nikitin at proc.ru>
  • Date: Sat, 15 Sep 2007 04:14:27 -0400 (EDT)

Dear Jean-Marc,
 Thank you very much for your answer!  I already made such assumptions but,
unfortunately, my problem wasn't solve. It is strange, because if I
prescribe for parameters m and n specific meaning Mathematica gave me very
nice results. For example:

In[2]:= n = 5;
            m = 2;
            HAp[p_]:= \!\(\(-\(1\/h\)\) - \(\((\(\(-h\) + p\)\/\(h +
p\))\)\^\(m - 2\ n\)\ \((h + \
                                p)\)\^2\)\/\(h\ \((h - p)\)\ p\)\)
            InverseLaplaceTransform[HAp[p], p, x]


Out[9] = \!\(\(-1\) +
               4\/315\ \[ExponentialE]\^\(h\ x\)\ \((1575 + 12600\ h\ x +
               31500\ h\^2\ x\^2 + 33600\ h\^3\ x\^3 + 18060\ h\^4\ x\^4 +
               208\ h\^5\ x\^5 + 812\ h\^6\ x\^6 + 64\ h\^7\ x\^7 +
               2\ h\^8\ x\^8)\)\)

        Should you tell me please why it is happence?

Alexey.






----- Original Message -----
From: "Jean-Marc Gulliet" <jeanmarc.gulliet at gmail.com>
To: "Alexey Nikitin" <nikitin at proc.ru>; <mathgroup at smc.vnet.net>
Sent: Thursday, September 13, 2007 9:08 PM
Subject: [mg81201] Re: Problem with inverse laplace transform (FIX)


> Alexey Nikitin wrote:
>
> <snip>
>
>>    I have 3 parameters h,m,n. Parameters m and n are integers. I tried to
>> find inverse Laplace transform of function:
>> InverseLaplaceTransform[-1/h - ((((-h+p)/(h+p))^(m-2n)) * (h+p)^2)  / 
>> (h*(h-p)*p),p,x]
>>
>> *-*-*-*-*- Mathematica code *-*-*-*-*
>>
>> \!\(InverseLaplaceTransform[\(-\(1\/h\)\) - \(\((\(\(-h\) + p\)\/\(h +
>> p\))\)\
>> \^\(m - 2\ n\)\ \((h + p)\)\^2\)\/\(h\ \((h - p)\)\ p\), p, x]\)
>>
>> -*-*-*-*-*--*-*-*-*-*--*-*-*-*-*--*-*-*-*-*--*
>>
>> but mathematica can not give me an answer. Can it be solved by
>> Mathematica?
>
> Though I do not know if this solve your problem, you can add assumptions
> to the InverseLaplaceTransform(like you can do with Integrate for
> instance). At least the documentation says so but the Front-End stubbornly
> (rightly?) colors everything after the x in flashy red...
>
> InverseLaplaceTransform[-1/
>    h - ((((-h + p)/(h + p))^(m - 2 n))*(h + p)^2)/(h*(h - p)*p), p, x,
>   Assumptions -> {m, n} \[Element] Integers && m > 0 && n > 0]
>
> HTH,
> --
> Jean-Marc



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