Re: Help on FindRoot

*To*: mathgroup at smc.vnet.net*Subject*: [mg5798] Re: [mg5786] Help on FindRoot*From*: seanross at worldnet.att.net*Date*: Wed, 22 Jan 1997 00:44:09 -0500*Sender*: owner-wri-mathgroup at wolfram.com

Hossein Kazemi wrote: > > I have the following lines: > > h[0]=1; > x[t_]:=2^h[t] - 3*h[t-1]; > Table[h[t]=h[t]/.FindRoot[x[t]==t,{h[t],2}],{t,1,5}] > > As you can see, I am trying to solve for different values of h[t], which > is recursively depends on h[t-1]. > > MMA (3.0) gives a bunch of errors such as > Unset:: norep: Assignment on h for h[1] not found. > and so on. > > However, it also gives the correct answers at the end. > > What is going on? Am I doing something wrong? > > ********************************************************** > Hossein Kazemi > University of Massachusetts Your function definition is not truly recursive. You define h[0], so when I call x[1], I need to know h[1] and h[0]. I would try re-defining the problem so that you used something like: h[t]=z/.FindRoot[2^z -3 h[t-1]==t,{z,2}]. I have tested this code, but it seems like you are asking for a result before calculating it. I would try and avoid doing root searches on the symbol h[t].