How can I get the mathematical expression for a specific constraint id?

In my log, as shown below, I see that the initial incumbent solution violates constraint R212895/R42845. I want to know which constraint is this or the mathematical expression associated with this constraint. How can I retrieve it?

Thanks

Gurobi Optimizer version 10.0.2 build v10.0.2rc0 (linux64)

CPU model: AMD EPYC 7763 64-Core Processor, instruction set [SSE2|AVX|AVX2]
Thread count: 16 physical cores, 16 logical processors, using up to 16 threads

Optimize a model with 212165 rows, 77908 columns and 590482 nonzeros
Model fingerprint: 0x9bab3eed
Variable types: 55968 continuous, 21940 integer (21578 binary)
Coefficient statistics:
  Matrix range     [1e-03, 1e+05]
  Objective range  [6e-02, 6e-02]
  Bounds range     [1e+00, 3e+00]
  RHS range        [1e-02, 6e+07]

User MIP start did not produce a new incumbent solution
User MIP start violates constraint R42845 by 0.057142857
MIP start from previous solve did not produce a new incumbent solution
MIP start from previous solve violates constraint R212895 by 4.000000000

Presolve removed 211073 rows and 76468 columns
Presolve time: 2.60s
Presolved: 1092 rows, 1440 columns, 4764 nonzeros
Variable types: 1254 continuous, 186 integer (186 binary)
Found heuristic solution: objective 24.5714014
Root barrier log...

Ordering time: 0.00s

Barrier statistics:
 AA' NZ     : 5.160e+03
 Factor NZ  : 2.888e+04 (roughly 1 MB of memory)
 Factor Ops : 1.693e+06 (less than 1 second per iteration)
 Threads    : 1

                  Objective                Residual
Iter       Primal          Dual         Primal    Dual     Compl     Time
   0  -1.25259726e+03 -6.23094227e+03  1.05e+02 8.35e-02  1.67e+01     3s
   1  -3.53857784e+01 -3.42188876e+03  4.01e+00 8.31e-02  1.93e+00     3s
   2   6.10459328e+00 -4.08104077e+02  4.65e-01 2.71e-03  2.00e-01     3s
   3   7.69909404e+00 -4.24086445e+01  4.22e-02 1.53e-04  2.22e-02     3s
   4   2.48137905e+00 -3.92943961e+00  1.67e-04 4.16e-16  2.72e-03     3s
   5   9.18955195e-01  6.09666024e-01  2.12e-06 2.22e-16  1.31e-04     3s
   6   8.75793516e-01  8.72806625e-01  2.61e-11 2.22e-16  1.27e-06     3s
   7   8.75463888e-01  8.75457958e-01  4.69e-12 2.22e-16  2.51e-09     3s
   8   8.75463125e-01  8.75463125e-01  8.15e-12 4.44e-16  2.53e-15     3s

Barrier solved model in 8 iterations and 2.83 seconds (2.16 work units)
Optimal objective 8.75463125e-01


Restart crossover...


Root relaxation: objective 8.754631e-01, 77 iterations, 0.06 seconds (0.02 work units)
Another try with MIP start

    Nodes    |    Current Node    |     Objective Bounds      |     Work
 Expl Unexpl |  Obj  Depth IntInf | Incumbent    BestBd   Gap | It/Node Time

H    0     0                       0.8754631    0.87546  0.00%     -    2s
     0     0    0.87546    0    1    0.87546    0.87546  0.00%     -    2s

Explored 1 nodes (77 simplex iterations) in 2.88 seconds (2.18 work units)
Thread count was 16 (of 16 available processors)

Solution count 2: 0.875463 24.5714 

Optimal solution found (tolerance 0.00e+00)
Best objective 8.754631250005e-01, best bound 8.754631250005e-01, gap 0.0000%

Marika Karbstein

Gurobi Staff

February 23, 2024 09:27
Edited

You can use the write method to write out your models to a human-readable format
```
model.write("myLP.lp")
```
You can open the file myLP.lp in any standard text editor and search for the constraint name.
Or:

You write a script in a similar way as discussed How do I access the left-hand side of a constraint?, for example

import gurobipy as gp
m=gp.read("data/glass4.mps")
m.read("sol.sol")
m.update()

con = m.getConstrByName("c15")
lexpr = m.getRow(con)
lhs = 0
for i in range(lexpr.size()):
    coeff = lexpr.getCoeff(i)
    var = lexpr.getVar(i)
    lhs += coeff * var.Start

print(f"{m.getRow(con)} {con.Sense} {con.RHS}")
print(f"{lhs} {con.Sense} {con.RHS}")

How can I get the mathematical expression for a specific constraint id?

Comments

Didn't find what you were looking for?