# JuMP COPT does not solve LP relaxation of MILP with SOS1 constraints
**URL:** https://discourse.julialang.org/t/jump-copt-does-not-solve-lp-relaxation-of-milp-with-sos1-constraints/102373
**Category:** Optimization (Mathematical)
**Tags:** jump
**Created:** [August 1, 2023, 9:00pm UTC](https://discourse.julialang.org/t/jump-copt-does-not-solve-lp-relaxation-of-milp-with-sos1-constraints/102373 "2023-08-01T21:00:15Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@Stuart\_Rogers](https://discourse.julialang.org/u/Stuart_Rogers)
#### Post date: [August 1, 2023, 9:00pm UTC](https://discourse.julialang.org/t/jump-copt-does-not-solve-lp-relaxation-of-milp-with-sos1-constraints/102373/1 "2023-08-01T21:00:15Z")
When I use COPT through JuMP to solve the LP relaxation of a MILP with SOS1 constraints, the MILP rather than its LP relaxation is solved. If the SOS1 constraints are removed, then COPT solves the LP relaxation.
Output:
$ julia JuMP\_solve.jl
Cardinal Optimizer v6.5.7. Build date Jul 28 2023
Copyright Cardinal Operations 2023. All Rights Reserved
Setting parameter ‘LogToConsole’ to 1
Setting parameter ‘LpMethod’ to 2
Model fingerprint: aa3dc1e0
Using Cardinal Optimizer v6.5.7 on Linux
Hardware has 24 cores and 48 threads. Using instruction set X86\_NATIVE (1)
Minimizing a MIP problem
The original problem has:
294515 rows, 299698 columns and 888526 non-zero elements
100 SOSs
Presolving the problem
The presolved problem has:
294515 rows, 299698 columns and 888526 non-zero elements
294414 binaries
Starting the MIP solver with 32 threads and 64 tasks
```
Nodes Active LPit/n IntInf BestBound BestSolution Gap Time
0 1 -- 0 0.000000e+00 -- Inf 184s
```
H 0 1 – 0 0.000000e+00 1.280000e+06 100.0% 184s
H 0 1 – 0 0.000000e+00 4.053610e+05 100.0% 184s
0 1 – 197 1.722190e+05 4.053610e+05 57.5% 199s
H 0 1 – 197 1.722190e+05 2.002380e+05 14.0% 201s
0 1 – 291 1.722675e+05 2.002380e+05 14.0% 221s
0 1 – 271 1.722696e+05 2.002380e+05 14.0% 238s
0 1 – 293 1.723109e+05 2.002380e+05 13.9% 255s
0 1 – 289 1.723154e+05 2.002380e+05 13.9% 273s
Julia code in JuMP\_solve.jl:
using JuMP
#using SCIP
#using HiGHS
using COPT
MPS\_fn = “/data/stuart/gen\_MPS\_files/p12\_fix0\_MILP\_binary\_SOS1\_x.mps”
model = read\_from\_file(MPS\_fn)
#opt = SCIP.Optimizer
#opt = HiGHS.Optimizer
opt = COPT.Optimizer
relax\_integrality(model)
set\_optimizer(model,opt)
set\_attribute(model,“LpMethod”,2)
@time optimize!(model)
---
### Author:  [@odow](https://discourse.julialang.org/u/odow)
#### Post date: [August 1, 2023, 9:47pm UTC](https://discourse.julialang.org/t/jump-copt-does-not-solve-lp-relaxation-of-milp-with-sos1-constraints/102373/2 "2023-08-01T21:47:48Z")
Per the docstring of `relax_integrality`, it does not remove SOS constraints: [JuMP · JuMP](https://jump.dev/JuMP.jl/stable/api/JuMP/#JuMP.relax_integrality)