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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