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
>
>
>
>
>