Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2002
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2002

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Unexpected result with RSolve?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg33636] Re: [mg33629] Unexpected result with RSolve?
  • From: Andrzej Kozlowski <andrzej at platon.c.u-tokyo.ac.jp>
  • Date: Thu, 4 Apr 2002 19:39:54 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Mathematica is right and you are wrong. If a[n + 1] == n a[n] and 
a[0]==1 then a[1]==0 a[0]  which is 0, and hence a[n] is 0 for all n>0. 
Of course the correct equation is:

In[11]:=
RSolve[{a[n + 1] == (n+1) a[n], a[0] == 1}, a[n], n]

Out[11]=
{{a[n]->n!}}

Andrzej Kozlowski

Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/

On Thursday, April 4, 2002, at 08:09  AM, 
wouter.van.den.broeck at vub.ac.be wrote:

> Hey,
>
> There's probably a sound solution, but i'm struggling to grab it:
>
> RSolve[{a[n + 1] == n a[n], a[0] == 1}, a[n], n]
>
> returns:
> {{a[n] -> 0}}
>
> where, i believe it 'should' return
> {{a[n] -> (n-1)!}}
>
> Anyone care to give me some directions as to why this 'unexpected'
> result?
>
> (note: I started of with the standard textbook example:
> RSolve[{a[n] == n a[n-1], a[0] == 1}, a[n], n]
> which returns
> {{a[n] -> n!}}
> so there's no need to correct me in this direction, I just explored a
> bit, and wonder why i'm getting that result with the variation above)
>
> TIA
>
> wouter vdb
>
>
>
>
>



  • Prev by Date: WorldGraphics Question
  • Next by Date: RE: MakeExpression
  • Previous by thread: RE: Unexpected result with RSolve?
  • Next by thread: Re: Unexpected result with RSolve?