Problems with FindRoot and recursive functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg89641] Problems with FindRoot and recursive functions*From*: "Daniel Kuang Chen Liu" <dkliu1 at student.monash.edu.au>*Date*: Mon, 16 Jun 2008 06:39:03 -0400 (EDT)

Hello, I have a recursive function of the form >> x1[t_] := If[t < 0, {t, 1}, 0.5 + x1[t - 1]] which returns a list of length 2, and the first element has a root at t=0.5 >> In[3]:= x1[0.5] >> Out[3]= {0., 1.5} I want to use FindRoot to determine t0 such that x1[t0][[1]] == 0, so I use the following code >> FindRoot[x1[t][[1]] == 0, {t, 0.5}] to which Mathematica complains During evaluation of In[6]:= FindRoot::nlnum: The function value {False} is not a list of numbers with dimensions {1} at {t} = {0.5}. It would much appreciated if someone could tell me what is wrong with the code. Daniel Liu

**Follow-Ups**:**Re: Problems with FindRoot and recursive functions***From:*"Daniel Kuang Chen Liu" <dkliu1@gmail.com>

**Re: Problems with FindRoot and recursive functions***From:*Murray Eisenberg <murray@math.umass.edu>