[AMPL 2059] Indicator constraints

classic Classic list List threaded Threaded
3 messages Options
Reply | Threaded
Open this post in threaded view
|

[AMPL 2059] Indicator constraints

davewoodrow

Hi,

I understand AMPL supports the use of indicator constraints (I use
CPLEX), but I am struggling to find text on how to use these
constraints in AMPL.  I cannot find material in the 2nd edition of the
AMPL book.  If anyone could help me it would be very much appreciated.

Also, would it always be beneficial to use indicator constraints
instead of bigM formulations with AMPL/CPLEX?

Thank you
Dave

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "AMPL Modeling Language" group.
To post to this group, send email to [hidden email]
To unsubscribe from this group, send email to [hidden email]
For more options, visit this group at http://groups.google.com/group/ampl?hl=en
-~----------~----~----~----~------~----~------~--~---

Reply | Threaded
Open this post in threaded view
|

[AMPL 2061] Re: Indicator constraints

Paul A. Rubin



On Nov 4, 10:34 am, [hidden email] wrote:
> Hi,
>
> I understand AMPL supports the use of indicator constraints (I use
> CPLEX), but I am struggling to find text on how to use these
> constraints in AMPL.  I cannot find material in the 2nd edition of the
> AMPL book.  If anyone could help me it would be very much appreciated.

http://www.ampl.com/INFORMS06.pdf has a presentation by Bob Fourer
that includes information and an example.
>
> Also, would it always be beneficial to use indicator constraints
> instead of bigM formulations with AMPL/CPLEX?

Fundamentally, that depends on how good (tight) an M you can suss out
on your own.  As I understand it, CPLEX will essentially convert the
indicator constraints into a bigM type formulation, using presolver
logic to estimate a suitable M.  What I was told (by someone at ILOG)
is that if I can come up with a reasonable value for M, I'm probably
better of using my estimate rather than using indicator constraints.

/Paul
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "AMPL Modeling Language" group.
To post to this group, send email to [hidden email]
To unsubscribe from this group, send email to [hidden email]
For more options, visit this group at http://groups.google.com/group/ampl?hl=en
-~----------~----~----~----~------~----~------~--~---

Reply | Threaded
Open this post in threaded view
|

[AMPL 2075] Re: Indicator constraints

davewoodrow

Thanks Paul,

your response is most appreciated.

On 6 Nov, 14:20, Paul <[hidden email]> wrote:

> On Nov 4, 10:34 am, [hidden email] wrote:
>
> > Hi,
>
> > I understand AMPL supports the use of indicator constraints (I use
> > CPLEX), but I am struggling to find text on how to use these
> > constraints in AMPL.  I cannot find material in the 2nd edition of the
> > AMPL book.  If anyone could help me it would be very much appreciated.
>
> http://www.ampl.com/INFORMS06.pdfhas a presentation by Bob Fourer
> that includes information and an example.
>
>
>
> > Also, would it always be beneficial to use indicator constraints
> > instead of bigM formulations with AMPL/CPLEX?
>
> Fundamentally, that depends on how good (tight) an M you can suss out
> on your own.  As I understand it, CPLEX will essentially convert the
> indicator constraints into a bigM type formulation, using presolver
> logic to estimate a suitable M.  What I was told (by someone at ILOG)
> is that if I can come up with a reasonable value for M, I'm probably
> better of using my estimate rather than using indicator constraints.
>
> /Paul

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "AMPL Modeling Language" group.
To post to this group, send email to [hidden email]
To unsubscribe from this group, send email to [hidden email]
For more options, visit this group at http://groups.google.com/group/ampl?hl=en
-~----------~----~----~----~------~----~------~--~---