Re: [Help-glpk] Different constraint for first element of a set than for other elements

[Noli Sicad]

Hi Marc,

Could you show us the constraint that make this error as well as the
data sets for these 3 sets so we can fix it.

Anyway, here is example how to this period in months:

~~~~~~~~~~
set MONTHS;

param Land_Coef{m in MONTHS, i in CROP};
param Forest_Coef{m in MONTHS,j in FORCROP};

var Land{i in CROP};

# constraint
#subject to LandAllocation(Months): Crop - ForestCrop <= TotalArea

subject to LandAllo{m in MONTHS}:
      sum{i in CROP} Land_Coef[m,i] * Land[i] -  sum{j in FORCROP}
Forest_Coef[m,j] * LandForest[j] <= TotalArea;

data;
set MONTHS:= Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec;

~~~~~~~~~~

Regards, Noli

On 2/2/10, Marc Goetschalckx <address@hidden> wrote:
> The model has a different constraint for the first element of a set (say
> PERIODS) than for all remaining elements.
> I have defined three sets:
> INITIAL_PERIOD;
> OTHER_PERIODS;
> PERIODS := INITIAL_PERIOD union OTHER_PERIODS;
> when MathProg is generating the model and specifically constraints over
> the PERIODS set it terminates with the following error
>
> cannot convert JAN to floating-point number
>
> where JAN is the first period in OTHER_PERIODS
> How should the model be written in MathProg to allow different
> constraints for the first element.
> Thanks
>