# Which solvers have dual solutions available for MINLPs?

**URL:** <https://discourse.julialang.org/t/which-solvers-have-dual-solutions-available-for-minlps/98859>\
**Category:** Optimization (Mathematical)\
**Tags:** jump\
**Created:** [May 15, 2023, 5:28am UTC](https://discourse.julialang.org/t/which-solvers-have-dual-solutions-available-for-minlps/98859 "2023-05-15T05:28:34Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![vineetjnair9](https://avatars.discourse-cdn.com/v4/letter/v/96bed5/32.png) [@vineetjnair9](https://discourse.julialang.org/u/vineetjnair9)\
**Post date:** [May 15, 2023, 5:28am UTC](https://discourse.julialang.org/t/which-solvers-have-dual-solutions-available-for-minlps/98859/1 "2023-05-15T05:28:34Z")

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Which solvers (out of the ones here - [Installation Guide · JuMP](https://jump.dev/JuMP.jl/stable/installation/)) can I extract dual values for, specifically for MINLPs? I was able to extract them while running Ipopt for NLPs but now I’m working on an MINLP (nonconvex) - I’m able to solve the problem using SCIP/Juniper but neither gives me access to duals. Any idea which solver I can use?

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**Author:** ![odow](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/odow/32/28685_2.png) [@odow](https://discourse.julialang.org/u/odow)\
**Post date:** [May 15, 2023, 6:31am UTC](https://discourse.julialang.org/t/which-solvers-have-dual-solutions-available-for-minlps/98859/2 "2023-05-15T06:31:06Z")

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MINLPs do not have dual solutions because they contain discrete variables.

Can you give an example of a MINLP with the “dual” that you expect?

See also [Computing the duals of a mixed-integer program · JuMP](https://jump.dev/JuMP.jl/stable/tutorials/linear/mip_duality/)

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**Author:** ![vineetjnair9](https://avatars.discourse-cdn.com/v4/letter/v/96bed5/32.png) [@vineetjnair9](https://discourse.julialang.org/u/vineetjnair9)\
**Post date:** [May 17, 2023, 7:04pm UTC](https://discourse.julialang.org/t/which-solvers-have-dual-solutions-available-for-minlps/98859/3 "2023-05-17T19:04:13Z")

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Ok thank you! I used the approach you suggested by resolving the continuous program with the fixed optimal integer solutions and it worked well. I was interested in getting the duals of power balance & flow limit constraint in the grid reconfiguration/switching problem.