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in my model I have the binary variable $f_{ij}$ which pushes a time-dependent $j$ integer variable $D_{ij}$ to zero if $f_{ij}$ takes the value 1 and keeps the integer number if $f_{ij}$ equals 0. Yes, I have linearised it accordingly. The variable $f_{ij}$ is currently coded like this. It takes the value 1 if the additional binary variable $z_{ij}$ was always zero in the last $\alpha$ days.

\begin{align} &(1-f_{ij})\le\sum_{t=j-\alpha}^{j-1}z_{it}&\quad\forall i\in I, j\in \{1+\alpha,\ldots,J\} \\ &M\cdot (1-f_{ij})\ge \sum_{t=j-\alpha}^{j-1}z_{it}&\quad\forall i\in I, j\in \{1+\alpha,\dots,J\} \end{align}

In addition to zero, I want to introduce that the variable $f_{ij}$ can also take the value 1 if the third binary variable $x_{ij}$ was zero in each of the last $\beta$ days. How can I additionally model this?

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  • $\begingroup$ I guess you can write your first constraint around $D$ as: $D_{i,j} = j(1-f_{i,j}) \ \ \ \forall j \in \{\alpha,...J\}$ $\endgroup$ Commented Apr 7 at 2:20

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Your second constraint is an aggregation of $$f_{ij}\le 1-z_{it}$$ for $t\in\{j-\alpha,\dots,j-1\}$, which enforces the logical implication $$f_{ij}\implies \lnot z_{it}.$$ To instead enforce $$f_{ij}\implies (\lnot z_{it}\lor \lnot x_{it}),$$ impose $$f_{ij}\le (1-z_{it})+(1-x_{it}).$$

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  • $\begingroup$ Thanks and this sole constraint ensures that $f$ is one if one or both conditions hold but is always zero if neiter holds? $\endgroup$ Commented Apr 6 at 17:29
  • $\begingroup$ No, it enforces that if $f=1$ then either $x=0$ or $z=0$. $\endgroup$
    – RobPratt
    Commented Apr 6 at 17:35

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