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For questions about mathematical optimization problems involving binary or general integer variables.

15 votes
3 answers
1k views

How does the search space affect the speed of an ILP solver?

Let us suppose we have an optimization problem which we have modeled as an ILP. Suppose we solve this problem using some set of constraints which restricts the search space. Let us suppose we model th …
ephemeral's user avatar
  • 917
2 votes
4 answers
121 views

Linearity of an optimization problem which comprises the product of variables with constant ...

In a mathematical integer optimization problem, if the objective function is represented as $\sum x_k \cdot M_k$, where $M_k$ is a non-linear function whose value is known and just plugged in to the o …
ephemeral's user avatar
  • 917
12 votes
2 answers
647 views

Expressing a chain of boolean ORs using ILP

How to express a chain of OR operations in an ILP in which each expression is a less than or equal constraint and the left hand side variable in all inequalities is always the same? All the variables …
ephemeral's user avatar
  • 917
1 vote
1 answer
99 views

Setting constant values in constraints depending on actual values of variables

We have a set of constraints in an ILP of the following form : $ \gamma (X_{11} + X_{12} + X_{13}) \leq C_1$ where $X_{ij} \in \{0,1\}$ and the value of $\gamma$ is going to depend on the actual value …
ephemeral's user avatar
  • 917
0 votes
2 answers
85 views

ILP constraint conditional on a value of a variable

If $X_{ijklm}$ are Boolean Variables, where $i,j,k,l,m$ range from $1$ to $n$, then write an ILP constraint to ensure that for each value of $k$, either all the $jth$ variables are set to $0$ or all t …
ephemeral's user avatar
  • 917
6 votes
1 answer
657 views

ILP Constraint to ensure exactly one constraint from a set of constraints is satisfied

Consider several Integer (0/1) ILP variables, i.e., Boolean variables, $x_i$'s. Consider an ILP constraint $x_1 + x_2 + x_3 \geq 1$ and another constraint $x_4 + x_5 + x_6 \geq 1$. I would like to rep …
ephemeral's user avatar
  • 917
11 votes
1 answer
525 views

Expressing a chain of boolean ORs using ILP involving different variables

How can I express a chain of OR operations in an ILP, given that each operand is an inequality between two binary variables? I have asked a similar question here: Chain of Boolean ORs. In that questio …
ephemeral's user avatar
  • 917
12 votes
2 answers
667 views

Expressing an implication as ILP where each implication term comprises a chain of boolean ORs

Consider an implication of the form $A \implies B$ where both $A, B$ comprises a chain of Boolean OR variables. For example, $(a_1 \lor a_2 \lor a_3) \implies (b_1 \lor b_2 \lor b_3)$. How can this b …
ephemeral's user avatar
  • 917
1 vote
2 answers
311 views

Linearizing if else conditions in ILP

We are given three binary indicator variables $X_{ij}, Y_{jk}$ and $Z_{jl}$. Write linear constraints such that, a) if $X_{ij}$ is equal to 1, then for that $j$ when $X_{ij} = 1$, exactly one $Y_{jk} …
ephemeral's user avatar
  • 917