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MathGroup Archive 2007

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Re: Two successive FindMinimum -> Bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74329] Re: [mg74312] Two successive FindMinimum -> Bug?
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Mon, 19 Mar 2007 01:56:44 -0500 (EST)
  • Reply-to: hanlonr at cox.net

fxt[x_,t_]=(x^2-t)^2;

Reduce[fxt[x,t]==0,t]

t == x^2

tminx should be restricted to numeric arguments

tminx[x_?NumericQ]:=t/.FindMinimum[fxt[x,t],{t,1}][[2]];

tminabs=FindMinimum[tminx[x],{x,1}]

{0., {x -> 7.450580485901526*^-9}}


Bob Hanlon

---- Dmitry Garanin <dgaranin at yahoo.com> wrote: 
> Hi All,
> 
> I am trying to solve a problem that requires application of FindMinimum (or similar rutines two times and it does not work. Here is a simplified example:
> 
> 
> fxt[x_,t_]=(x^2-t)^2  (* Searching for a minimal t for which fxt turns to zero *)
> tminx[x_]:=t/.FindMinimum[fxt[x,t],{t,1}][[2]] (* Finding the minimizing t for a given x *)
> tminabs=FindMinimum[tminx[x],{x,1}]  (* Minimizing this t with respect to x. The result should be tminabs=0 at x=0 *)
> 
> The last command here does not work since, evidently tminx[x] (that is x^2 for us humans) is not treated as a regular function.
> 
> Is there a bug here or I am doing something wrong??
> 
> Help is appreciated.
> 
> 
> http://profiles.yahoo.com/dgaranin
> 



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