Re: sum of recursive fn: solving for n
- To: mathgroup at smc.vnet.net
- Subject: [mg22144] Re: sum of recursive fn: solving for n
- From: "P.J. Hinton" <paulh at wolfram.com>
- Date: Wed, 16 Feb 2000 02:35:07 -0500 (EST)
- Organization: "Wolfram Research, Inc."
- References: <888afd$c7p@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On 14 Feb 2000, AC fiona wrote:
> what am i doing wrong here?
>
> f[x_] := (f[x-1])*2
> f[1] =2
> Solve[Sum[f[x], {x, 1,n}] ==62, n]
You're doing the programmatic equivalent of beating a nail with a wrench.
Try using recursion to solve your problem.
In[1]:=
n = 1;
seedvalue = 2;
summation = 2;
NestWhile[
(n++; term = 2 #; summation += term; term) &,
seedvalue,
(#; summation < 62) &
] ;
n
Out[1]=
5
--
P.J. Hinton
Mathematica Programming Group paulh at wolfram.com
Wolfram Research, Inc.
Disclaimer: Opinions expressed herein are those of the author alone.