[Coin-ipopt] How to choose objective functions from multi-objective functions

[Claudia D'Ambrosio]

Hi Rui,
I think that what Rodrigo suggested is OK with Ipopt.
Otherwise, what I usually do is defining the 
problem with both the objective functions using 
the "problem" keyword, then switch between the 
two objective functions using the "drop" and 
"restore" keywords ("restore" to resume a dropped 
objective function). I'm sure this trick is OK with Ipopt.
Regards,
Claudia


At 02.25 22/05/2007, Rodrigo López Negrete de la Fuente wrote:
>Hi Rui,
>
>In your ampl model, have you tried using the 
>objective command, as described in
><http://groups.google.com/group/ampl/browse_thread/thread/1b6ab5cdfb462ee4>http://groups.google.com/group/ampl/browse_thread/thread/1b6ab5cdfb462ee4 
>
>
>Because, as Andreas just mentioned, Ipopt can 
>only handle one objective function at a time. 
>I've been using ampl's named problems with Ipopt 
>without any trouble, but I'm only specifying one 
>objective function per problem.
>
>hth,
>   Rodrigo.
>
>On 5/21/07, Andreas Waechter 
><<mailto:andreasw at watson.ibm.com> andreasw at watson.ibm.com> wrote:
>Hi Rui,
>
>I think that we wrote the AMPL interface in Ipopt so that it complains (in
>the way you describe) when there are more than one objective functions in
>the model.   Maybe the trick that Michal mentioned already does the trick
>for you.
>
>If not, please submit a ticket at the Ipopt trac page and attach the AMPL
>model that give you trouble.
>
>Thanks,
>
>Andreas
>
>On Sun, 20 May 2007, Michal Kaut wrote:
>
> > Hello,
> >
> > you can use named problems, using the "problem" keyword. This is one of the
> > new features of AMPL, so you won't find it in 
> the first edition of the book.
> > For a detailed description, including examples, see
> > <http://ampl.com/NEW/loop2.html>http://ampl.com/NEW/loop2.html
> >
> > Regards,
> > Michal Kaut
> >
> >
> > Rui Huang wrote:
> >> Hello
> >>
> >> I have two objective functions.
> >> So I have two same ampl models, except that each one has a different
> >> objective function.
> >> and try to solve them together without "reset"
> >> But ampl breaks
> >> "There is more than one objective function in the AMPL model, but
> >> AmplTNLP::set_active_objective has not been called",
> >>
> >> I do not know how to call this function.
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>--
>Rodrigo López Negrete
><http://muon.blogdns.org/%7Erush/>http://muon.blogdns.org/~rush/
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