modifying equations

[Archiver]

Hi,

I'm trying to maximize for a specific column in a matrix. I've been
able to do that easily just by defining z and maximizing for it.
However, I want to now, maximize for each column in an iterative
fashion using loop.

I can't quite figure out how to do this because I can't modify
equation after first defining as column 1 for example.

How would I go about changing that?

Thanks
AB
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[Archiver]

AB4166 wrote:
> Hi,
>
> I'm trying to maximize for a specific column in a matrix. I've been
> able to do that easily just by defining z and maximizing for it.
> However, I want to now, maximize for each column in an iterative
> fashion using loop.
>
> I can't quite figure out how to do this because I can't modify
> equation after first defining as column 1 for example.
>
> How would I go about changing that?
>
> Thanks
> AB
> --~--~---------~--~----~------------~-------~--~----~
> To post to this group, send email to gamsworld@googlegroups.com
> To unsubscribe from this group, send email to gamsworld+unsubscribe@googlegroups.com
> For more options, visit this group at http://groups.google.com/group/gamsworld?hl=en
> -~----------~----~----~----~------~----~------~--~---
>

Assuming you have z as the obj var, you could define z using some data that you change in the loop. For example,

set J 'all columns' / j1 * j100 /;
set JJ(J) 'objective col';

equation o;
o.. z =e= sum{JJ, x(JJ)};

loop {J,
JJ = NO;
JJ(J) = YES;
solve yourModel max z using LP;
};

Something like this will do the job.

--
Steven Dirkse, Ph.D. GAMS Development Corporation
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