I am solving a mixed integer linear program in Java using Cplex Java API. After cplex solver has solved the problem, I want to know how many branch-and-bound nodes were explored in the process. However, when I use the function cplex.getNnodes() (where cplex is an IloCplex object), I get 0 regardless of the problem instance.

What could be going wrong? Is there any other way to access the number of nodes explored by Cplex for finding the solution?

If it helps, here is the Cplex log for a problem instance.

CPXPARAM_Simplex_Tolerances_Optimality 1.0000000000000001e-09

CPXPARAM_Read_APIEncoding "UTF8"

CPXPARAM_MIP_Interval 10

CPXPARAM_MIP_Strategy_VariableSelect 1

Found incumbent of value 339.000000 after 0.01 sec. (0.24 ticks)

Tried aggregator 3 times.

MIP Presolve eliminated 3 rows and 18 columns.

MIP Presolve modified 1726 coefficients.

Aggregator did 17 substitutions.

Reduced MIP has 320 rows, 5289 columns, and 17880 nonzeros.

Reduced MIP has 5289 binaries, 0 generals, 0 SOSs, and 0 indicators.

Presolve time = 0.06 sec. (37.17 ticks)

Tried aggregator 1 time.

Reduced MIP has 320 rows, 5289 columns, and 17880 nonzeros.

Reduced MIP has 5289 binaries, 0 generals, 0 SOSs, and 0 indicators.

Presolve time = 0.02 sec. (11.80 ticks)

Probing time = 0.03 sec. (3.76 ticks)

Clique table members: 335.

MIP emphasis: balance optimality and feasibility.

MIP search method: dynamic search.

Parallel mode: deterministic, using up to 4 threads.

Root relaxation solution time = 0.07 sec. (45.35 ticks)

Nodes Cuts/

Node Left Objective IInf Best Integer Best Bound ItCnt Gap

* 0+ 0 339.0000 14.0000 95.87%

* 0+ 0 329.0000 14.0000 95.74%

* 0+ 0 143.0000 14.0000 90.21%

0 0 115.2587 151 143.0000 115.2587 842 19.40%

0 0 116.2790 198 143.0000 Cuts: 87 1024 18.69%

0 0 116.4667 200 143.0000 Cuts: 33 1134 18.55%

* 0+ 0 120.0000 116.4667 2.94%

0 0 116.5124 191 120.0000 Cuts: 38 1240 2.91%

0 0 116.5436 167 120.0000 Cuts: 25 1331 2.88%

0 0 116.5844 136 120.0000 Cuts: 22 1436 2.85%

0 0 116.5951 233 120.0000 Cuts: 14 1516 2.84%

0 0 116.6005 247 120.0000 Cuts: 18 1589 2.83%

0 0 116.6031 240 120.0000 Cuts: 9 1612 2.83%

* 0+ 0 119.0000 116.6031 2.01%

* 0+ 0 118.0000 116.6031 1.18%

* 0+ 0 117.0000 116.6031 0.34%

0 0 cutoff 117.0000 116.6031 1612 0.34%

Elapsed time = 2.07 sec. (715.08 ticks, tree = 0.01 MB, solutions = 6)

Clique cuts applied: 53

Zero-half cuts applied: 45

Gomory fractional cuts applied: 10

Root node processing (before b&c):

Real time = 2.08 sec. (715.58 ticks)

Parallel b&c, 4 threads:

Real time = 0.00 sec. (0.00 ticks)

Sync time (average) = 0.00 sec.

Wait time (average) = 0.00 sec.

------------

Total (root+branch&cut) = 2.08 sec. (715.58 ticks)