Wednesday, January 28, 2009

Cplex log: number of integer variables

Sometimes progress logs pose some interesting questions. In the Cplex log below we solve a problem with 2016 binary variables (after presolving). However the progress log seems to indicate that when we start 2036 of them are integer infeasible.

Reading data...
Starting Cplex...
Tried aggregator 1 time.
MIP Presolve eliminated 45077 rows and 15073 columns.
MIP Presolve modified 504 coefficients.
Aggregator did 1008 substitutions.
Reduced MIP has 73884 rows, 26656 columns, and 201936 nonzeros.
Reduced MIP has 2016 binaries, 0 generals, 0 SOSs, and 0 indicators.
Presolve time = 0.45 sec.
Clique table members: 900.
MIP emphasis: hidden feasible solutions.
MIP search method: dynamic search.
Parallel mode: opportunistic, using up to 4 threads.
Parallel mode: opportunistic, using up to 4 threads for concurrent optimization.
Using devex.
Using devex.

Total real time on 4 threads = 16.18 sec.
Root relaxation solution time = 16.19 sec.

Nodes Cuts/
Node Left Objective IInf Best Integer Best Node ItCnt Gap

0 0 0.0000 2036 0.0000 20


  1. Do you also know what generals and indicators are?

  2. Yes: generals are general integer variables, and indicators are somewhat special to Cplex; they can be used to model implications. The Cplex documentation contains more information.