Relaxing integrality on specific index values of a variable

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1

Hi, I have the following variable in my .mod:

var X {CKLLT} >= 0;

Which is defined in the .dat file as:

set CKLLT :=
(commodity1, vehicle, location1, location2, time)
(commodity2, vehicle, location1, location2, time)
…

As you can see, the variable X is continuous. However, I would like to know if it is possible to force integrality for one of the commodities in the X{CKLLT} set. For example, when C in CKLLT =“commodity2”, the variable X must be integer, but the rest of the X variable solutions where the commodity does not equal “commodity2” can be continuous.

Thanks!

2

You can define the variables as integer, and then use AMPL’s builtin .relax suffix to specify the ones that should be treated as continuous. For example,

var X {CKLLT} integer >= 0;
let {(c,v,l1,l2,t) in CKLLT: c <> "commodity2"} 
   X[c,v,l1,l2,t].relax := 1;