# Gurobi Error 10005: Unable to retrieve attribute 'Pi'

**URL:** <https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691>\
**Category:** Optimization (Mathematical)\
**Tags:** jump, gurobi\
**Created:** [January 20, 2021, 11:06pm UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691 "2021-01-20T23:06:22Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![rezabayani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rezabayani/32/25954_2.png) [@rezabayani](https://discourse.julialang.org/u/rezabayani)\
**Post date:** [January 20, 2021, 11:06pm UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/1 "2021-01-20T23:06:22Z")

</div>

I am trying to retrieve some Gurobi attributes for through MOI.get() function with direct\_model() enabled. Everything seems to be working but when I try to get “Pi” (dual value for a constraint), I encounter the error:

```julia
Gurobi Error 10005: Unable to retrieve attribute 'Pi'
in top-level scope at initial_test.jl:53
in get at JuMP\e0Uc2\src\JuMP.jl:889
in get at Gurobi\Lci9Q\src\MOI_wrapper.jl:3657
in _get_attribute at Gurobi\Lci9Q\src\MOI_wrapper.jl:3619
in _check_ret at Gurobi\Lci9Q\src\MOI_wrapper.jl:277

```

```julia
versioninfo():
Commit 2d5741174c (2019-12-30 21:36 UTC)
Platform Info:
OS: Windows (x86_64-w64-mingw32)
CPU: Intel(R) Core(TM) i7-9700K CPU @ 3.60GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.1 (ORCJIT, skylake)
Environment:
JULIA_EDITOR = "C:\Users\Reza\AppData\Local\atom\app-1.54.0\atom.exe" -a
JULIA_NUM_THREADS = 4

Pkg.status():
`C:\Users\Reza\.julia\environments\v1.3\Project.toml`
[c52e3926] Atom v0.12.30
[fa961155] CEnum v0.3.0
[be33ccc6] CUDAnative v3.1.0
[8f4d0f93] Conda v1.5.0
[7806a523] DecisionTree v0.10.10
[31c24e10] Distributions v0.23.8
[587475ba] Flux v0.10.4
[60bf3e95] GLPK v0.14.5
[61eb1bfa] GPUCompiler v0.2.0
[2e9cd046] Gurobi v0.9.7
[7073ff75] IJulia v1.23.1
[b6b21f68] Ipopt v0.6.5
[4076af6c] JuMP v0.21.4
[e5e0dc1b] Juno v0.8.4
[1902f260] Knet v1.3.6
[91a5bcdd] Plots v1.6.12
[438e738f] PyCall v1.92.2
[3646fa90] ScikitLearn v0.6.3
[2913bbd2] StatsBase v0.33.2
[9a3f8284] Random

```

steps to reproduce:

```julia
using Gurobi
using JuMP

# define a simple UC problem

n_u = 8
n_t = 4
U = collect(1:n_u) # num units
T = collect(1:n_t) # num time steps
p_g_min = round.(0.3 <em>rand(n_u), digits=2)
p_g_max = 1 .+ round.(rand(n_u), digits=2)
cost_g = 10 .+ round.(10.0</em> rand(n_u), digits=1)
cost_g0 = round.(3.0 <em>rand(n_u), digits=1)
d0 = rand((sum(p_g_min):.01:.5</em> sum(p_g_max)),n_t)

# basic_uc_model = Model(Gurobi.Optimizer)

basic_uc_model = direct_model(Gurobi.Optimizer())
    @variable(basic_uc_model, p_g[i in U, t in T])
    @variable(basic_uc_model, I_g[i in U, t in T], Bin)
    @constraint(basic_uc_model, lower_band[i in U, t in T], p_g[i,t] >= p_g_min[i]*I_g[i,t])
    @constraint(basic_uc_model, upper_band[i in U, t in T], p_g[i,t] <= p_g_max[i]*I_g[i,t])
    @constraint(basic_uc_model, demand[t in T], sum(p_g[i,t] for i in U) == d0[t])
    @objective(basic_uc_model, Min, sum(p_g[i,t]*cost_g[i] + I_g[i,t]*cost_g0[i] for i in U, t in T))

optimize!(basic_uc_model)
JuMP.objective_value(basic_uc_model)
JuMP.value.(p_g)
JuMP.value.(I_g)

MOI.get(basic_uc_model, Gurobi.ModelAttribute("ObjVal")) # Objective value for current solution
MOI.get(basic_uc_model, Gurobi.VariableAttribute("Obj"), p_g[2,2]) # Linear objective coefficient
MOI.get(basic_uc_model, Gurobi.ConstraintAttribute("Slack"), lower_band[2,2]) #
MOI.get(basic_uc_model, Gurobi.ConstraintAttribute("Pi"), upper_band[2,2]) # Dual value (also known as the shadow price)

```

I can obtain other attributes as can be seen, this only happens when I try “Pi”. Also, I tried different versions of Gurobi (version 8.1 gurobi software with according julia gurobi package, instead of 9.1) but it did not help. I even tried it on both JuliaPro and Atom+Juno but that did not help neither. Finally, this is not certainly a syntax issue since if I change “Pi” with a random name that is not included, e.g. “Dual”, the error code changes : **Gurobi Error 10004: Unknown attribute ‘Dual’**. I would appreciate your feedback.

---

<div class="post-metadata">

**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:** [January 20, 2021, 11:11pm UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/2 "2021-01-20T23:11:16Z")

</div>

Please provide a link when cross-posting: [https://github.com/jump-dev/Gurobi.jl/issues/390](https://github.com/jump-dev/Gurobi.jl/issues/390).

As I explained, dual values are not available for models with binary variables.

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<div class="post-metadata">

**Author:** ![rezabayani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rezabayani/32/25954_2.png) [@rezabayani](https://discourse.julialang.org/u/rezabayani)\
**Post date:** [January 20, 2021, 11:18pm UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/3 "2021-01-20T23:18:51Z")

</div>

Thank you for your responses and I appreciate you bearing with me. I am going to delete this post if possible.

---

<div class="post-metadata">

**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:** [January 20, 2021, 11:51pm UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/4 "2021-01-20T23:51:34Z")

</div>

No need to delete. It may be helpful for others. The link for cross posting is just so that two people don’t reply with the same answer to a question in two places.

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<div class="post-metadata">

**Author:** ![Yunus\_Kovankaya](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yunus_kovankaya/32/29523_2.png) [@Yunus\_Kovankaya](https://discourse.julialang.org/u/Yunus_Kovankaya)\
**Post date:** [September 28, 2021, 3:58am UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/5 "2021-09-28T03:58:50Z")

</div>

This post was super helpful to me as I ran into the same issue today. Thank you 🙂

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<div class="post-metadata">

**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:** [September 28, 2021, 4:09am UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/6 "2021-09-28T04:09:49Z")

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Glad to hear!

A reminder to future readers that you should query `dual_status(model)` to see if the solver has a solution _ **before** _ querying `dual` or `shadow_price`. Not doing so can throw an error or silently return incorrect solutions.

Relevant section in the JuMP documentation: [Solutions · JuMP](https://jump.dev/JuMP.jl/stable/manual/solutions/#Dual-solutions)

---

<div class="post-metadata">

**Author:** ![WalterMadelim](https://avatars.discourse-cdn.com/v4/letter/w/3e96dc/32.png) [@WalterMadelim](https://discourse.julialang.org/u/WalterMadelim)\
**Post date:** [December 8, 2024, 2:41pm UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/7 "2024-12-08T14:41:28Z")

</div>

This situation is more rare, but I encounter it anyway.

```julia
Set parameter OutputFlag to value 1
Set parameter QCPDual to value 1
Gurobi Optimizer version 11.0.2 build v11.0.2rc0 (win64 - Windows 11.0 (22631.2))

CPU model: 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz, instruction set [SSE2|AVX|AVX2|AVX512]
Thread count: 4 physical cores, 8 logical processors, using up to 8 threads

Optimize a model with 528 rows, 288 columns and 2047 nonzeros
Model fingerprint: 0x2b227fd8
Model has 24 quadratic constraints
Coefficient statistics:
  Matrix range [1e-03, 6e+00]
  QMatrix range [1e+00, 1e+00]
  Objective range [2e-01, 2e+01]
  Bounds range [0e+00, 0e+00]
  RHS range [5e-02, 5e+00]
Presolve removed 370 rows and 107 columns
Presolve time: 0.00s
Presolved: 158 rows, 204 columns, 485 nonzeros
Presolved model has 24 second-order cone constraints
Ordering time: 0.00s

Barrier statistics:
 AA' NZ : 4.190e+02
 Factor NZ : 1.458e+03
 Factor Ops : 1.652e+04 (less than 1 second per iteration)
 Threads : 1

                  Objective Residual
Iter Primal Dual Primal Dual Compl Time
   0 -1.25354714e+02 -3.75702206e+03 1.76e+01 2.10e+01 1.18e+02 0s
   1 3.53382960e+02 -2.86354426e+03 4.14e-01 2.63e+00 1.59e+01 0s
   2 2.45527260e+02 -4.03372205e+02 2.32e-03 3.77e-01 2.52e+00 0s
   3 8.35773331e+01 -7.05132949e+01 2.17e-04 6.90e-02 5.49e-01 0s
   4 3.88871083e+01 1.27671608e+01 1.85e-05 1.03e-02 8.99e-02 0s
   5 3.43244850e+01 2.55418767e+01 5.42e-06 3.41e-03 2.99e-02 0s
   6 3.25598824e+01 2.88231832e+01 1.57e-06 1.48e-03 1.28e-02 0s
   7 3.19555238e+01 3.14579383e+01 4.31e-07 6.49e-05 1.55e-03 0s
   8 3.17528802e+01 3.16894458e+01 8.10e-08 1.04e-06 1.89e-04 0s
   9 3.17077557e+01 3.17046971e+01 4.17e-09 1.28e-08 9.05e-06 0s
  10 3.17054821e+01 3.17051501e+01 3.91e-09 9.95e-10 9.82e-07 0s

Barrier solved model in 10 iterations and 0.01 seconds (0.00 work units)
Optimal objective 3.17054821e+01

Warning: failed to compute QCP dual solution due to inaccurate barrier solution
         Try decreasing BarQCPConvTol for more accuracy

User-callback calls 101, time in user-callback 0.00 sec

```

---

<div class="post-metadata">

**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:** [December 8, 2024, 8:11pm UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/8 "2024-12-08T20:11:25Z")

</div>

> [@WalterMadelim](#):
>
> ```julia
> Warning: failed to compute QCP dual solution due to inaccurate barrier solution
> Try decreasing BarQCPConvTol for more accuracy
> 
> ```

@WalterMadelim did you follow the instructions in this warning?

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<div class="post-metadata">

**Author:** ![WalterMadelim](https://avatars.discourse-cdn.com/v4/letter/w/3e96dc/32.png) [@WalterMadelim](https://discourse.julialang.org/u/WalterMadelim)\
**Post date:** [December 22, 2024, 10:08am UTC](https://discourse.julialang.org/t/gurobi-error-10005-unable-to-retrieve-attribute-pi/53691/9 "2024-12-22T10:08:55Z")

</div>

No, I decided to use Mosek instead.  
It appears that Mosek’s dual is more reliable when we are dealing with Conic programs.