I apologize for not following the rules. The code for my actual problem using the hints by Bill Simpson follows. Unfortunately I seem to not be able to think of a simple example.
This is the solution to the problem I posted earlier today using the code for the actual problem.
The functions and input paramaters are defined in another notebook.
gf\[Beta][{x_, \[Beta]_}] :=
Module[{x1, x2, xtst, fnw, f1, xnw}, xtst = Total[x]/2;
fnw = LAcr[xtst, 1/12., LAI, LBI, AF, a, b, c, d,
400000., \[Alpha]0, \[Beta]];
f1 = LAcr[x[[1]], 1/12., LAI, LBI, AF, a, b, c, d,
400000., \[Alpha]0, \[Beta]];
Return[If[Sign[fnw] == Sign[f1], {xtst, x[[2]]}, {x[[1]], xtst}]];]
f1 = LAcr[x[[1]], 1/12., LAI, LBI, AF, a, b, c, d,
400000., \[Alpha]0, \[Beta]];
Return[If[Sign[fnw] == Sign[f1], {xtst, x[[2]]}, {x[[1]], xtst}]];]`
f[x_] := gf\[Beta][{x, .6}]
t works slightly differently from previously. What used to work, doesn't.
In[27]:= NestWhile[f, {500., 50000.}, test &]
Out[27]= {500., 50000.}
However, if I add a large integer it does.
In[28]:= NestWhile[f, {500., 50000.}, test &, 100]
Out[28]= {35964.7, 35964.7}
The integer seems to be the number of iterations.`enter code here`
In[29]:= NestWhile[f, {500., 50000.}, test &, 3]
Out[29]= {25250., 37625.}