pulp reports Infeasible for Unbounded HiGHS MIPs #894
Description
Details for the issue
Pulp incorrectly reports infeasible for Primal infeasible/Unbounded MIPs solved with HiGHs. Unbounded LPs work fine.
What did you do?
I ran the script:
import pulp
# Problem formulation
m = pulp.LpProblem("myProblem", pulp.LpMinimize)
var_cont = pulp.LpVariable("var_cont", lowBound=None, upBound=None, cat=pulp.LpContinuous)
var_int = pulp.LpVariable("var_int", lowBound=0, upBound=1, cat=pulp.LpInteger)
m += var_cont + var_int
m.solve(
pulp.HiGHS(
timeLimit=30,
gapRel=0.01,
threads=1,
msg=True,
log_to_console=True,
)
)
print("Status:", pulp.LpStatus[m.status])
assert m.status == pulp.LpStatusUnbounded
What did you expect to see?
<some solver logs>
Status: Unbounded
What did you see instead?
Running HiGHS 1.12.0 (git hash: 755a8e0): Copyright (c) 2025 HiGHS under MIT licence terms
MIP has 0 rows; 2 cols; 0 nonzeros; 1 integer variables (1 binary)
Presolving model
Presolve: Primal infeasible or unbounded
Src: B => Branching; C => Central rounding; F => Feasibility pump; H => Heuristic;
I => Shifting; J => Feasibility jump; L => Sub-MIP; P => Empty MIP; R => Randomized rounding;
S => Solve LP; T => Evaluate node; U => Unbounded; X => User solution; Y => HiGHS solution;
Z => ZI Round; l => Trivial lower; p => Trivial point; u => Trivial upper; z => Trivial zero
Nodes | B&B Tree | Objective Bounds | Dynamic Constraints | Work
Src Proc. InQueue | Leaves Expl. | BestBound BestSol Gap | Cuts InLp Confl. | LpIters Time
0 0 0 0.00% -inf inf inf 0 0 0 0 0.0s
Solving report
Status Primal infeasible or unbounded
Primal bound inf
Dual bound -inf
Gap inf
P-D integral 0
Solution status -
Timing 0.00
Max sub-MIP depth 0
Nodes 0
Repair LPs 0
LP iterations 0
Status: Infeasible
Traceback (most recent call last):
File "C:\Temp\bad_reported_value.py", line 20, in <module>
assert m.status == pulp.LpStatusUnbounded
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError
Useful extra information
The info below often helps, please fill it out if you're able to. :)
What operating system are you using?
- Windows: ( version: 11)
- Linux: ( distro: ___ )
- Mac OS: ( version: ___ )
- Other: ___
I'm using python version:
- 3.7
- 3.8
- 3.9
- 3.10
- 3.11
- Other: 3.12.3
I installed PuLP via:
- pypi (python -m pip install pulp)
- github (python -m pip install -U git+https://github.com/coin-or/pulp)
- Other: ___ (conda?)
Relevant package versions
PuLP==3.3.0
highspy==1.12.0
Did you also
- Tried out the latest github version: https://github.com/coin-or/pulp
- Searched for an existing similar issue: https://github.com/coin-or/pulp/issues?utf8=%E2%9C%93&q=is%3Aissue%20