# Quick way to find tight constraints?

**URL:** <https://discourse.julialang.org/t/quick-way-to-find-tight-constraints/5975>\
**Category:** Optimization (Mathematical)\
**Tags:** jump\
**Created:** [September 19, 2017, 3:13pm UTC](https://discourse.julialang.org/t/quick-way-to-find-tight-constraints/5975 "2017-09-19T15:13:46Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Halil1](https://avatars.discourse-cdn.com/v4/letter/h/d9b06d/32.png) [@Halil1](https://discourse.julialang.org/u/Halil1)\
**Post date:** [September 19, 2017, 3:13pm UTC](https://discourse.julialang.org/t/quick-way-to-find-tight-constraints/5975/1 "2017-09-19T15:13:47Z")

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Hello all,

Is there a straight-forward method for understanding which constraints of the model are tight?

I will run some scenarios which I will change multiple parameters at a time, so just curious if there is any quick way to check that without changing parameters one by one.

Thanks for your help!

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**Author:** ![juliohm](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/juliohm/32/215266_2.png) [@juliohm](https://discourse.julialang.org/u/juliohm)\
**Post date:** [September 20, 2017, 5:01pm UTC](https://discourse.julialang.org/t/quick-way-to-find-tight-constraints/5975/2 "2017-09-20T17:01:47Z")

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@Halil1 this is a traditional problem in optimization. The Lagrange multipliers give you the sensitivity to the constraints. I suggest you to read Boyd’s book or watch his video lectures for more information: [Convex Optimization – Boyd and Vandenberghe](https://web.stanford.edu/~boyd/cvxbook)

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**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [September 20, 2017, 7:27pm UTC](https://discourse.julialang.org/t/quick-way-to-find-tight-constraints/5975/3 "2017-09-20T19:27:08Z")

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To follow up on that, the `JuMP` function `getdual()` when called on a JuMP constraint (the thing returned by `@constraint`) will retrieve those Lagrange multipliers.