ClpSimplex::initialSolve() not giving reproducible results after an infeasible model

[ukrishnas]

Hi,

I have two models m3 (feasible), and m2 (infeasible). If I execute m3, m2, m3, then the first and second execution of m3 deviate in the solution vector. I can see the perturbation in the 2nd execution is changing. The behavior is reproducible through clp standalone, and am showing the output below. Appreciate, if somebody could explain why this is happening, and if there is a workaround.

Thanks.
Umesh.

Repeated execution of feasible model (m3) is reproducible

Coin LP version trunk, build Dec 14 2021
Clp takes input from arguments ( - switches to stdin)
Enter ? for list of commands or help
Clp:import m3.mps
At line 1 NAME ClpDefau
At line 2 ROWS
At line 5231 COLUMNS
At line 145498 RHS
At line 148113 RANGES
At line 150728 ENDATA
Problem ClpDefau has 5227 rows, 28235 columns and 238152 elements
Model was imported from .\m3.mps in 0.246 seconds
Clp:duals
Special options 0
More special options 2
Perturbation = 50
Independent option 0 = 0
Independent option 1 = 32768
Independent option 2 = 3
Presolve type 0 passes 10
Presolve 3971 (-1256) rows, 28060 (-175) columns and 227693 (-10459) elements
Perturbing problem by 0.001% of 527000 - largest nonzero change 1.110609 ( 0.071783033%) - largest zero change 0
Optimal - objective value 3.0857591e+12
After Postsolve, objective 3.0857591e+12, infeasibilities - dual 0 (0), primal 0 (0)
Optimal objective 3.085759062e+12 - 5254 iterations time 0.552, Presolve 0.09

Same results on execution of allslack; duals or import; duals.

Infeasible model (m2)

Clp:import m2.mps
At line 1 NAME ClpDefau
At line 2 ROWS
At line 4562 COLUMNS
At line 12572 RHS
At line 14852 RANGES
At line 17095 ENDATA
Problem ClpDefau has 4558 rows, 808 columns and 14476 elements
Model was imported from .\m2.mps in 0.023 seconds
Clp:duals
Special options 0
More special options 2
Perturbation = 50
Independent option 0 = 0
Independent option 1 = 32768
Independent option 2 = 3
Presolve type 0 passes 10
Presolve 389 (-4169) rows, 779 (-29) columns and 5241 (-9235) elements
0 Obj 2.1711783e+10 Primal inf 10170039 (84)
Primal infeasible - objective value 6.8920254e+11
Presolved problem not optimal, resolve after postsolve
After Postsolve, objective 6.8920254e+11, infeasibilities - dual 30500 (3), primal 117.6451 (85)
0 Obj 7.5355324e+11 Primal inf 16520372 (177) Dual inf 4387500 (28)
Primal infeasible - objective value 6.8919935e+11
PrimalInfeasible objective 6.891993507e+11 - 545 iterations time 0.072, Presolve 0.00

Execution of first model deviates starting with the perturbation value

Clp:import m3.mps
At line 1 NAME ClpDefau
At line 2 ROWS
At line 5231 COLUMNS
At line 145498 RHS
At line 148113 RANGES
At line 150728 ENDATA
Problem ClpDefau has 5227 rows, 28235 columns and 238152 elements
Model was imported from .\m3.mps in 0.139 seconds
Clp:duals
Special options 0
More special options 2
Perturbation = 50
Independent option 0 = 0
Independent option 1 = 32768
Independent option 2 = 3
Presolve type 0 passes 10
Presolve 3971 (-1256) rows, 28060 (-175) columns and 227693 (-10459) elements
Perturbing problem by 0.001% of 527000 - largest nonzero change 1.1107645 ( 0.071677529%) - largest zero change 0
0 Obj 0 Primal inf 82048912 (3069)
Optimal - objective value 3.0857591e+12
After Postsolve, objective 3.0857591e+12, infeasibilities - dual 0 (0), primal 0 (0)
Optimal objective 3.085759062e+12 - 5350 iterations time 0.532, Presolve 0.07