> I am trying to write
> a model how to minimize the production cost
> given the total
> demand and production cost per production plant.
> The thing is that I
> don't want have all production plants in use as it is now given my
> model below.
> I would only like to start up a new plant when the demand of all
> the cheaper production isn't suffient.
> I think my problem
> is a mix of different kind of problems and not a pure minimize
> problem.
> Please, can someone
> help me out on this?
Probably you need to introduce binary variables:
var z{i in PLANTS}, binary;
where z[i] = 1 means that plant i is used, otherwise z[i] = 0. If plant
i is not used, it can produce nothing, therefore:
s.t. limits1{i in PLANTS} : p[i] >= z[i] * minlim[i];
s.t. limits2{i in PLANTS} : p[i] <= z[i] * maxlim[i];
/* for each plant within production limits */
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