topic Re: constraint declaration in Mathematical Optimization, Discrete-Event Simulation, and OR

constraint declaration

Santha — Wed, 03 Mar 2021 00:27:43 GMT

Hi I am having syntax error in the constraint declaration

The constraint that I want is to make sure that the model forces a specific combination. ie. IST-SAV-MAEU-SAV to be 1. Not sure how to sum the containers.

var IsPortsTransitLSPDC {Ports,Transit,LSP,DC} binary;

num IST_SAV;
fix IsPortsTransitLSPDC ['IST','SAV','MAEU','SAV']=1;
READ DATA STDOPT.PN3381_Data(where=(PortSource = "QIN" and RateMatchDest='SAV')) INTO IST_SAV=FEU;

/*Force IST to SAV via MAEU and SAV*/
CON IST_SAV_MAEU_SAV {p in {'IST'}, {t in {'SAV'}, c in {'MAEU'}, d in {'SAV'}}:
ContainersfromPortstoLSPtoDC ['QIN','SAV','MAEU','SAV'] =IST_SAV*IsPortsTransitLSPDC['IST','SAV','MAEU','SAV'];

Re: constraint declaration

Santha — Wed, 03 Mar 2021 00:28:55 GMT

oops. here is the constraint i have

/*Force IST to SAV via MAEU and SAV*/
CON IST_SAV_MAEU_SAV {p in {'IST'}, {t in {'SAV'}, c in {'MAEU'}, d in {'SAV'}}:
ContainersfromPortstoLSPtoDC ['IST','SAV','MAEU','SAV'] =IST_SAV*IsPortsTransitLSPDC['IST','SAV','MAEU','SAV'];

Re: constraint declaration

RobPratt — Wed, 03 Mar 2021 00:40:38 GMT

Sorry, I don't quite understand your question. The FIX statement will fix a variable to a given value, and your syntax for that looks correct. Where does the sum come in?

Re: constraint declaration

Santha — Wed, 03 Mar 2021 00:46:53 GMT

Rob

yeah i want that specific variable to be set 1 when the combo is IST-SAV-MAEU-SAV.

In order to do that i declare a binary variable IsPortsTransitLSPDC and set it as 1. And also trying to set up a constraint so that this variable is used correctly and that the flow through this combo is exactly we see in my other variable IST_SAV that I have.

Re: constraint declaration

Santha — Wed, 03 Mar 2021 03:12:32 GMT

Tried this one as well: Feels am close but not yet

CON CONST_IST_SAV {p in {'IST'}, d in {'SAV'}}: 
sum {t in Transit,c in LSP} ContainersfromPortstoLSPtoDC['IST',t,c,'SAV'] =IST_SAV*IsPortsTransitLSPDC['IST','SAV','MAEU','SAV'];

Re: constraint declaration

Santha — Wed, 03 Mar 2021 04:23:17 GMT

CON CONST_IST_SAV {p in {'IST'}, d in {'SAV'},c in {'LSP'}}: 
sum {t in Transit} ContainersfromPortstoLSPtoDC['IST',t,'MAEU','SAV'] =IST_SAV*IsPortsTransitLSPDC['IST','SAV','MAEU','SAV'];

based on your feedback, i tweaked and this one worked.

Re: constraint declaration

RobPratt — Fri, 05 Mar 2021 15:54:42 GMT

I'm glad you got it working. Because you don't use p, d, or c anywhere, here's a simpler way to declare the same constraint:

CON CONST_IST_SAV:
sum {t in Transit} ContainersfromPortstoLSPtoDC['IST',t,'MAEU','SAV'] =IST_SAV*IsPortsTransitLSPDC['IST','SAV','MAEU','SAV'];