[AMPL 2801] Initial Condition for CPLEX

[Excel Wanabe]

Hello AMPL gurus,

I am trying to solve an LP using initial conditions and for some
reason, it keeps ignoring them. Can anyone please help me?

Initial Condition:
-----------------------
for {g in ogs } {
  let f_gs[g] :=  m_gs[g];
}

General Model:
----------------------
Param targets
Var x
Var slack, surplus
s.t. (target-x)-slack+surplus = 0
min sum(slack+surplus)

I write this out to binary (write bflex)
Use CPLEX to solve

If I change the let expression, I get the same solution, in the same
number of iterations.

Please note, I have read the discussion on “Defining initial guess for
Donlp2 solver” to no avail.

Does anyone have any ideas?

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

[Robert Fourer-2]

The linear programming algorithms used by CPLEX do not make use of initial
values of the variables.  CPLEX's simplex methods do have the ability to
make use of initial basis status information, as described in section 14.2
of the AMPL book (or at www.ampl.com/NEW/statuses.html).

Bob Fourer
4er@...

> -----Original Message-----
> From: ampl@... [mailto:ampl@...]
> On Behalf Of Excel Wanabe [rgavish@...]
> Sent: Wednesday, September 09, 2009 10:51 AM
> To: AMPL Modeling Language
> Subject: [AMPL 2801] Initial Condition for CPLEX
>
>
> Hello AMPL gurus,
>
> I am trying to solve an LP using initial conditions and for some
> reason, it keeps ignoring them. Can anyone please help me?
>
> Initial Condition:
> -----------------------
> for {g in ogs } {
>   let f_gs[g] :=  m_gs[g];
> }
>
> General Model:
> ----------------------
> Param targets
> Var x
> Var slack, surplus
> s.t. (target-x)-slack+surplus = 0
> min sum(slack+surplus)
>
> I write this out to binary (write bflex)
> Use CPLEX to solve
>
> If I change the let expression, I get the same solution, in the same
> number of iterations.
>
> Please note, I have read the discussion on "Defining initial guess for
> Donlp2 solver" to no avail.
>
> Does anyone have any ideas?
>
>

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