       Re: RSolve question

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

```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:=
> RSolve[{
> k*(1 + k)*a[k] + (1 + k)*(2 + k)*a[2 + k] == 0,
> a==0, a==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=
> RSolve[{k (1 + k) a[k] + (1 + k) (2 + k) a[2 + k] == 0,
>    a == 0, a == 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
solution
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
http://www.princon.com/princon/
Tel: (500) PRN-CPIA

```

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