       Re: FindMinimum Problem

• To: mathgroup at smc.vnet.net
• Subject: [mg44707] Re: FindMinimum Problem
• From: Jiang Xiao <jiang.xiao at physics.gatech.edu>
• Date: Fri, 21 Nov 2003 05:13:29 -0500 (EST)
• Organization: Georgia Institute of Technology
• References: <bpa1rv\$19t\$1@smc.vnet.net> <bpd1bi\$c9c\$1@smc.vnet.net> <bpffpl\$lv6\$1@smc.vnet.net> <bphuh2\$1on\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```yes, this works great, thank you guys.

Jiang

Bobby R. Treat wrote:
> This works for me using version 5.0:
>
> foo[x_?NumericQ] := x^2 - a*x /. First@
>       NDSolve[{a'[z] == x*z, a == 1}, a, {z, -1, 1}]
> FindMinimum[foo[x], {x, -1, 1}]
>
> {-0.166667, {x -> 0.333333}}
>
> Jens-Peer had left out "First@", so foo took on List values like {2.5}
> rather than just the number 2.5. It's also important to make the range
> {z,-1,1} encompass the range where a minimum might be found --
> especially the two initial starting points, which were 1 and -1 in his
> post.
>
> The pattern x_?NumericQ matches x if it is numeric -- as it will be
> when FindMinimum tries to iterate to a solution. If you don't use that
> pattern, you get an error message when FindMinimum tries a symbolic x
> value (which it does, for some reason I can't fathom).
>
> Bobby
>
> Jiang Xiao <jiang.xiao at physics.gatech.edu> wrote in message news:<bpffpl\$lv6\$1 at smc.vnet.net>...
>
>>thank you for replying, I tried it, but it still doesn't work.
>>what's the meaning of x_?NumericQ?
>>if I let foo[x_?NumericQ]:=x^2-x, findminimum can't get output either,
>>but no problem with foo[x_]:=x^2-x.
>>
>>Jiang
>>
>>Jens-Peer Kuska wrote:
>>
>>>Hi,
>>>
>>>you ust make a function
>>>
>>>foo[x_?NumericQ]:=x^2-a*x/.NDSolve[{a'[z]==x*z,a==1},a,{z,0,1}]
>>>
>>>FindMinimum[foo[x],{x,-1,1}]
>>>
>>>Regards
>>>  Jens
>>>
>>>Jiang Xiao wrote:
>>>
>>>
>>>>Hi, all,
>>>>   recently I am dealing with a problem as following, findminimum(over x)
>>>>of a function f[a,x], where a[z] satisfies a differential equation
>>>>a'[z]=x*z say. The code is like:
>>>>FindMinimum[x^2-a*x/.NDSolve[{a'[z]==x*z,a==1},a,{z,0,1}],{x,-1,1}]
>>>>
>>>>the problem is that I can do it in mathematica 4.2, but can't in mathematica
>>>>5.0 now. Do anybody where is the problem?
>>>>
>>>>thanks,
>>>>
>>>>Jiang
>>>
>>>
>

```

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