Re: Help: Switch constraints on or off

On 11/24/20 10:12 PM, Greg Gruber wrote:
> Hi Manuel,
>
> try setting StorageFlag to 1 or 0 as a parameter (based on your data),
> and then doing this:
>
>    subject to linctr14-1 {i in PeriodsCount: i == 1}:
>            StorageEnergy[i] >= StorageFlag*( existing constraint ) ;
>    subject to linctr14-0 {i in PeriodsCount: i == 1}:
>            StorageEnergy[i] <= StorageFlag*( existing constraint ) +
> (1-StorageFlag) * M   ;
>
> When StorageFlag = 1, these two constraints equate to your equality
> constraint.
> When StorageFlag = 0, the constraints just become bounds (0 and M). If
> you want to allow StorageEnergy[i] to be negative, you could add " -
> (1-StorageFlag)*M" to the first constraint.


This approach is adequate if StorageFlag is a binary *variable*. For a
*parameter* selecting constraints see
https://en.wikibooks.org/wiki/GLPK/Conditional_Constraints.

Best regards

Heinrich

>
> I *think* this will work -- good luck!
>
> Best regards,
> Greg
>
>
>     ---------------------------------------------------------------------
>
>     Message: 1
>     Date: Tue, 24 Nov 2020 18:59:09 +0000
>     From: Manuel Castro <[email protected] <mailto:[email protected]>>
>     To: "help-glpk" <[email protected] <mailto:[email protected]>>
>     Subject: Help: Switch constraints on or off
>     Message-ID: <[email protected]
>     <mailto:[email protected]>>
>     Content-Type: text/plain; charset="utf-8"
>
>     Hi there,
>
>
>
>     I am wondering how I can use an if statement to turn a constraint on
>     or off.
>
>     For example in my problem I have the following constraint:
>
>
>
>     subject to linctr14 {i in PeriodsCount: i == 1}: StorageEnergy[i] =
>     (StorageStateCharge * StorageEnergyRating +
>     ((StorageEfficiencyCharge * (StoragePowerCharge[i])) -
>     ((StoragePowerDischarge[i]) / StorageEfficiencyDischarge)));
>
>
>
>     Now, I only want to consider storage in my problem if an object
>     storage actually exists.
>
>     For that, I would have a StorageStatusFlag which if equal to "1"
>     then I would consider the constraint in my problem.
>
>     For example:
>
>
>
>     If (StorageStatusFlag == 1) then
>
>          subject to linctr14 {i in PeriodsCount: i == 1}:
>     StorageEnergy[i] = (StorageStateCharge * StorageEnergyRating +
>     ((StorageEfficiencyCharge * (StoragePowerCharge[i])) -
>     ((StoragePowerDischarge[i]) / StorageEfficiencyDischarge)));
>
>     end if
>
>
>     This is what I used to do in "mosel" language from FICO Xpress (I
>     don't have a license anymore so I am discovering GLPK ). How can I
>     do this in GLPK language? What's the workaround that we can use for
>     this?
>
>
>
>     Many thanks in advance for your help. It's really appreciated.
>
>
>
>     Kind regards,
>
>     Manuel.
>