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Re: Help with NMinimize

  • To: mathgroup at smc.vnet.net
  • Subject: [mg82374] Re: Help with NMinimize
  • From: Flavio <flavio.cimolin at gmail.com>
  • Date: Thu, 18 Oct 2007 05:04:52 -0400 (EDT)
  • References: <ff1qmk$9eq$1@smc.vnet.net><ff4fse$dre$1@smc.vnet.net>

Thank you for your answer, I'm learning Mathematica and I think I will
never stop doing it...

I realized just after sending the message to have written (to the
group) f[x,y,...] instead of f[x_,y_,...] , I'm sorry. Can you please
tell me where in the help I can find the difference between the
function declaration

f[x_,y_] :=

and your kind

f[{x_,y_}]:=

What's wrong with the first kind of declaration, which is used many
times in the examples?

Regards,

Flavio




On 17 Ott, 10:07, Szabolcs Horv=E1t <szhor... at gmail.com> wrote:
> You should learn the basics of Mathematica before you start using it.
> There are many good tutorials in the documentation.  At least work
> through the one titled "First five minutes with Mathematica".
>
> Flavio wrote:
> > Hi everybody, I can't figure out how to solve this problem with
> > NMinimize, which I want to use in order to test the Nelder and Mead
> > algorithm with an externally evaluated function.
>
> > I consider the following five argument function (of course this is not
> > my actual minimization function):
>
> > g[x1,x2,x3,x4,x5]:=Module[{xx1=x1,xx2=x2,xx3=x3,xx4=x4,xx5==
x5},
> > Export[ToString[xx1]<>".txt",xx1];
> > Return[(xx1-1)^2+(xx2-1)^2-xx3^2+(xx4+1)^2+xx5^2];
> > ]
>
> The correct definition of this function would be
>
> g[lst:{x1_, x2_, x3_, x4_, x5_} /; And @@ NumericQ /@ lst] :=
>    ( Export[ToString[x1]<>".txt", x1];
>      (x1-1)^2+(x2-1)^2-x3^2+(x4+1)^2+x5^2 )
>
> The condition for the argument pattern is used to ensure that NMinimize
> won't evaluate g with symbolic arguments.  Now you can use:
>
> NMinimize[{g[{x1,x2,x3,x4,x5}], constr},{x1,x2,x3,x4,x5}, Method->
> {"NelderMead",RandomSeed->1}]
>
>
>
>
>
> > Now, if I compute
>
> > g[1,2,3,4,5]
>
> > I get the correct answer "14", and a file named "1.txt" is created,
> > exactly as expected.
>
> > But if I use the NMinimize command in this way:
>
> > NMinimize[{g[x1,x2,x3,x4,x5],constr},{x1,x2,x3,x4,x5},Method-
> >> {"NelderMead",RandomSeed->1},EvaluationMonitor:>Print["x1=",x1]]
>
> > with these constraints:
>
> > constr={x1^2<=4&&x2^2<=4&&x3^2<=4&&x4^2<=4&&x5^2<=4};
>
> > The minimization is performed, but only a single file, named "x1.txt"
> > is created.
>
> > The x1 argument in the fuction seems to have the value "x1" rather
> > than its effective value? Can somebody explain me which is the problem
> > with my code, and how can I actually use the value inside the
> > function?
> > I need to use this value because the function g should be replaced by
> > a function that creates a file with the arguments, evaluate a command,
> > and then reads the values obtained by the external program.
>
> Please read the tutorial tutorial/ExternalPrograms too.  You could use
> RunThrough[], or something simpler, like Get["!progname " <>
> ToExpression[x1]].
>
> > Thank you very much for your help.
>
> > Flavio Cimolin
>
> --
> Szabolcs




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