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Re: RSolve question

  • To: mathgroup at
  • Subject: [mg5546] Re: RSolve question
  • From: "David B. Wagner" <dbwagner at>
  • Date: Thu, 19 Dec 1996 01:02:38 -0500
  • Organization: Principia Consulting
  • Sender: owner-wri-mathgroup at

Daitaro Hagihara wrote:
> To the List:
> I appreciate if you can give me some input into the following math
> questions that puzzle me quite a bit:
> 1) Why am I getting the following error?  This example came from
> Wolfram Koepf's PowerSeries`.  You don't need this package here.
> In[2]:=
> RSolve[{
> k*(1 + k)*a[k] + (1 + k)*(2 + k)*a[2 + k] == 0,
> a[0]==0, a[1]==1}, a[k], k]
> DSolve::dnim:
>    Built-in procedures cannot solve this differential
>      equation.
> DSolve::dnim:
>    Built-in procedures cannot solve this differential
>      equation.
> Out[2]=
> RSolve[{k (1 + k) a[k] + (1 + k) (2 + k) a[2 + k] == 0,
>    a[0] == 0, a[1] == 1}, a[k], k]

The error you're getting is a consequence of his package; it doesn't
happen if his package isn't loaded.  RSolve can't solve this recurrence,
so Kopf's package tries to take over for it; if you read Kopf's article
carefully (I'm recalling this from memory, mind you), the whole point
of his technique is that he tranlates the problem of finding the 
to a recurrence into the problem of finding a solution to a differential
equation.  It allows some new classes of recurrences to be solved,
but is limited by the power of the built-in DSolve function.

		Dave Wagner
		Principia Consulting
		Tel: (500) PRN-CPIA

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