Confronting dates in a constrain

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Erika 2024-2-26

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评论： Eric Sofen 2024-2-28

I am implementing an optimisation problem on matlab and one of the constraints imposes an inequality of the type: date(x) * decision variable> date(y) + duration

Obviously I cannot multiply a date by a number so how could I solve the problem?

Thanks in advance for the help!

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Walter Roberson 2024-2-26

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移动：Walter Roberson 2024-2-26

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Perhaps

decision_variable * (date(x) > date(y) + duration)

leading to

date(y) - date(x) + duration

multiplied by something. But the something is not necessarily the decision variable: it depends on what the intent is when the decision variable is false, whether that is intended to cause the constraint to pass or to fail.

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Erika 2024-2-28

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@Eric Sofen This is the code related to the constrain I was talking about:

for n=1:Nr
    for k=1:Nr
        if (k ~= n)
            for v=1:Vr
                temp=f(n)+hours(eps(n,k)/mu);
                constr_combined_time(n,k,v)=datenum(q(k))*y(n,k,v)>=datenum(temp);
            end
        end
    end
end

the general meaning is that q(k) is the starting date of the job k multiplied by the decision variable which is zero if the job is not part of the optimal solution or it is equal to 1 if the job is executed because it is part of the optimal solution. Basically this date must be later than the finishing date of the job n to which job k is combined to (+ a certain duration).

I'm a beginner using Matlab but I tried implementing Walter's solution and It didn't work in this situation so I'm still using datenum which seems to work well in this particular case.

Eric Sofen 2024-2-28