# Solution foun by heuristic GLPK
**URL:** https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772
**Category:** Optimization (Mathematical)
**Created:** [May 4, 2020, 10:41pm UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772 "2020-05-04T22:41:50Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@lausilvag](https://discourse.julialang.org/u/lausilvag)
#### Post date: [May 4, 2020, 10:41pm UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/1 "2020-05-04T22:41:50Z")
Hi guys!
I am using GLPK solver for a MIP. The output terminal shows me the next information:
GLPK Simplex Optimizer, v4.64
16 rows, 120 columns, 800 non-zeros
1: obj = 4.548322148e+003 inf = 0.000e+000 (0)
-
```
9: obj = 3.270600000e+003 inf = 0.000e+000 (0)
```
OPTIMAL LP SOLUTION FOUND
GLPK Integer Optimizer, v4.64
16 rows, 120 columns, 800 non-zeros
120 integer variables, all of which are binary
Integer optimization begins…
-
```
9: mip = not found yet >= -inf (1; 0)
```
Solution found by heuristic: 3351
- 14: \>\>\>\>\> 3.330000000e+003 \>= 3.330000000e+003 0.0% (1; 3)
- 14: mip = 3.330000000e+003 \>= tree is empty 0.0% (0; 7)
INTEGER OPTIMAL SOLUTION FOUND
I don’t want him to use heuristics to find a solution and, I don’t know which parameter i should disable for this.
Do you have any idea how to disable the option: provide solution found by heuristic in GLPK.
Thanks for your help!
---
### Author:  [@joaquimg](https://discourse.julialang.org/u/joaquimg)
#### Post date: [May 5, 2020, 12:22am UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/2 "2020-05-05T00:22:17Z")
May I ask why you don’t want heuristics?
---
### Author:  [@odow](https://discourse.julialang.org/u/odow)
#### Post date: [May 5, 2020, 12:29am UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/3 "2020-05-05T00:29:45Z")
I’m not sure if GLPK has an option to turn all heuristics off.
I’ve moved your question to the `Optimization (Mathematical)` category.
---
### Author:  [@joaquimg](https://discourse.julialang.org/u/joaquimg)
#### Post date: [May 5, 2020, 12:32am UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/4 "2020-05-05T00:32:54Z")
anyway, you can always look at the manual: ftp://ftp.gnu.org/gnu/glpk/ …
it seems that the only heuristic ON by default is: simple rounding (sr\_heur)
---
### Author:  [@dragond4](https://discourse.julialang.org/u/dragond4)
#### Post date: [September 23, 2020, 8:16am UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/5 "2020-09-23T08:16:58Z")
Hi joaquimg,
sorry for replying to a post dating back 4 months, but I think there is at least one good reason for disabling the _simple rounding heuristic_ in GLPK.
Namely, there is a [known bug](https://en.m.wikibooks.org/wiki/GLPK/Callback_functions) with that heuristic and the lazy constraint callback in GLPK: if am not wrong, when a solution is found by the _simple rounding heuristic_, it is not checked for feasibility by invoking the lazy constraint callback.
The bug is reported at least until GLPK 4.60, but I experienced a similar issue with a more recent version of GLPK in Julia 1.5.0. This implies that if the solution found by _simple rounding heuristic_ satisfies the constraints in the model, it is considered (incorrectly) feasible also if some lazy constraints are in fact violated (just because…they are not checked).
In a branch-and-bound this may prune the search-tree nodes containing the correct optimal solution, thus reporting incorrect solutions.
The suggested workaround is to turn off the _simple rounding heuristic_, via flag `sr_heur` (which I did not find how to do in JuMP).
Thanks for your attention!
Michele
---
### Author:  [@joaquimg](https://discourse.julialang.org/u/joaquimg)
#### Post date: [September 23, 2020, 1:20pm UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/6 "2020-09-23T13:20:22Z")
There is a sketch on how to set parameters in: [https://github.com/jump-dev/GLPK.jl#glpkoptimizer](https://github.com/jump-dev/GLPK.jl#glpkoptimizer)
Thus you can do:
```julia
using JuMP, GLPK
model = Model(GLPK.Optimizer)
set_optimizer_attribute(model, "sr_heur", GLPK.GLP_OFF)
```
---
### Author:  [@dragond4](https://discourse.julialang.org/u/dragond4)
#### Post date: [September 23, 2020, 2:49pm UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/7 "2020-09-23T14:49:16Z")
Hi joaquimg,
thanks for your reply.
Unfortunately I was already aware of the sketch you sent me, on how to set GLPK parameters in JuMP.
It seems that the flag `sr_heur` is not supported by JuMP, or that the one you were referring to is not the correct way to do.
More precisely, trying
```julia
set_optimizer_attribute(model, "sr_heur", GLPK.GLP_OFF)
```
returns me the error:
> UndefVarError: GLP\_OFF not defined
> Stacktrace:
> [1] getproperty at .\Base.jl:26 [inlined]
Also trying with:
```julia
set_optimizer_attribute(model, "sr_heur", 0)
```
gives the error:
> MathOptInterface.UnsupportedAttribute{MathOptInterface.RawParameter}: Attribute MathOptInterface.RawParameter(“sr\_heur”) is not supported by the model.
> Stacktrace:
> [1] set(::GLPK.Optimizer, ::MathOptInterface.RawParameter, ::Int64) at .julia\packages\GLPK\oTTtu\src\MOI\_wrapper.jl:315
explicitly saying that `sr_heur` is not supported.
I did this tests on a machine running Windows 8.1, Julia 1.5.0 and GLPK v4.64.
Best regards,
Michele
---
### Author:  [@joaquimg](https://discourse.julialang.org/u/joaquimg)
#### Post date: [September 23, 2020, 5:13pm UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/9 "2020-09-23T17:13:21Z")
Please run:
] st
And paste results here.
It must be a version problem.
---
### Author:  [@joaquimg](https://discourse.julialang.org/u/joaquimg)
#### Post date: [September 23, 2020, 5:17pm UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/10 "2020-09-23T17:17:31Z")
I am on the latest versions:
JuMP 0.21.5
MathOptInterface 0.9.17
GLPK 0.14.2 (GLPK.jl the julia wrapper not GLPK itself)
---
### Author:  [@dragond4](https://discourse.julialang.org/u/dragond4)
#### Post date: [September 23, 2020, 8:04pm UTC](https://discourse.julialang.org/t/solution-foun-by-heuristic-glpk/38772/11 "2020-09-23T20:04:30Z")
Hello joaquimg,
thanks again for your support. This is the output you asked in a previous message (I keep only the relevant stuff):
> (@v1.5) pkg\> st
> Status `.julia\environments\v1.5\Project.toml`
> [a076750e] CPLEX v0.6.6
> [60bf3e95] GLPK v0.13.0
> [4076af6c] JuMP v0.21.3
You were 100% right: updating the JuMP and GLPK packages to the latest versions, the _simple rounding heuristic_ was successfully disabled as you suggested, using:
```julia
set_optimizer_attribute(model, "sr_heur", GLPK.GLP_OFF)
```
Best regards,
Michele