Let \(x_i\) be binary variables and \(a_i\) given positive integers.

I have an equality constraint like the following \[x_i\left(\sum_{j=1}^nx_{j}\right)=a_ix_i,\] for all \(i\).

This means that if \(x_i=1\), then there must exists a set \(S\) with cardinality \(|S|=a_i-1\) such that \(x_j=1\) for all \(j\in S\).

How can I linearize these constraints? If the constraints were of type inequality I could use a large (or small) number and write it as:

\[\left(\sum_{j=1}^nx_{j}\right)\leq a_ix_i+M(1-x_i),\] for all \(i\).

asked 18 Jan '18, 11:15

zbir's gravatar image

zbir
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accept rate: 0%

edited 18 Jan '18, 11:21


Hint: Think of your equality as two inequalities and apply your big-M approach twice.

Also, for numerical reasons be sure to choose \(M\) as small as possible.

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answered 18 Jan '18, 11:21

Rob%20Pratt's gravatar image

Rob Pratt
1.2k26
accept rate: 28%

edited 18 Jan '18, 11:22

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Asked: 18 Jan '18, 11:15

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Last updated: 18 Jan '18, 11:22

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