[AMPL 2612] change variable bound

[Ali Baharev]

I would like to change the upper bound of x[28] from 1.0 to 0.8 in

var x{ i in 1..1000} >= 0.1, <= 1.0;

How can i do that?

Any help is appreciated,

Ali

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[Yasin053]

I think you should add a constraint into your model that ensures that x[28] <=0.8.

Ali Baharev wrote:

I would like to change the upper bound of x[28] from 1.0 to 0.8 in

var x{ i in 1..1000} >= 0.1, <= 1.0;

How can i do that?

Any help is appreciated,

Ali

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[Ali Baharev]

Thanks.

Unfortunately I HAVE TO set the upper bound directly. Is there a way to do it?

Ali

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[Ali Baharev]

Sorry, it works, it is may fault, i just disabled presolve.

With presolve enabled, it gives the effect i was looking for.

Thank you very much!

Ali

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[Robert Fourer-2]

The best way to change an upper bound is to define a parameter to represent
it.  For example, in this case, you could say

   param x_ub > 0, default 1.0;
   var x {i in 1..1000} >= 0.1, <= x_ub;

Initially x_ub will be 1.0 by default, but you can change this bound to 0.8
by means of the command "let x_ub := 0.8;".

-- Bob

> -----Original Message-----
> From: ampl@... [mailto:ampl@...]
> On Behalf Of Ali Baharev [ali.baharev@...]
> Sent: Friday, June 26, 2009 9:23 AM
> To: ampl@...
> Subject: [AMPL 2612] change variable bound
>
>
> I would like to change the upper bound of x[28] from 1.0 to 0.8 in
>
> var x{ i in 1..1000} >= 0.1, <= 1.0;
>
> How can i do that?
>
> Any help is appreciated,
>
> Ali
>

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[Robert Fourer-2]

I didn't notice you only wanted to change the upper bound of x[28].  Of
course adding a constraint that x[28] <= 0.8 will work fine, as long as you
are always going to be trying to make the bound smaller.  But if you are
going to want to change bounds any way you like, then a more general way to
do it is

   param x_ub {1..1000} > 0, default 1.0;
   var x {i in 1..1000} >= 0.1, <= x_ub[i];
   ...
   let x_ub[28] := 0.8;

> -----Original Message-----
> From: Ali Baharev [mailto:ali.baharev@...]
> Sent: Wednesday, July 01, 2009 10:48 AM
> To: 4er@...
> Cc: ampl@...
> Subject: Re: [AMPL 2612] change variable bound
>
> Dear Profesor Fourer,
>
> Thank you for the response. Unfortunately, i am afraid i do not
> understand your proposal.
>
> I want all x[i]-s to have the upper bound 1.0 except x[28] which
> should have an upper bound 0.8. Yasin053's proposal with presolve
> enabled gives the expected result.
>
> Is there another way to do this?
>
> Many thanks,
>
> Ali

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