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[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 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