Originally posted by: Mathsg

Hi, 

while solving an MIP problem the CPLEX engine shows "Row 'c31' infeasible" i have gone through the posts and found that the problem is in my constraint but how to identify it and  where the problem is infeasible? then i get the help from preveious post to mention the name of constraint and then i labled all the constraint with the name. Now i have found where there is an error but i dont know how to fix it.  OPL studion show me an error of Infeasibility row (e.g., Infeasibility row 'SourceConst({0})(1)(1)':  0  = 1.).

 forall(i in flows, j in routes, u in nodes: u==i.src[u])
       SourceConst:
      sum(v in nodes)(lemda[i][j]-lemda[i][j])==1;
       forall(i in flows, j in routes, u in nodes: u==i.dest[u])
            DestConst:
      sum(v in nodes)(lemda[i][j]-lemda[i][j])==-1;
       forall(i in flows, j in routes, u in nodes: u!=i.src[u] && u!=i.dest[u])
          SDConst:
      sum(v in nodes)(lemda[i][j]-lemda[i][j])==0; 
     forall ( i in flows, u in nodes, v in nodes: u!=v)
       ctCover:
   sum( j in routes) lemda[i][j]<= 1;   

your help will be highly appreciated. thank you

Hi,

see technote https://www.ibm.com/support/pages/display-full-indices-or-real-map-item-name-variables-and-constraints

and then the relaxation will be easier to understand

regards

NB: Many how to with OPL at https://www.linkedin.com/pulse/how-opl-alex-fleischer/

Originally posted by: Mathsg

Hi Alex, 

I have done the changes and get the infeasible solution. 

Note that I modified the CPLEX default settings and change the BIG M value to 1000000.

Tried aggregator 1 time.
LP Presolve eliminated 134 rows and 14 columns.
Aggregator did 1 substitutions.
Reduced LP has 6 rows, 30 columns, and 60 nonzeros.
Presolve time = 0.00 sec. (0.07 ticks)

Iteration log . . .
Iteration:     1   Dual objective     =             1.000000
Tried aggregator 1 time.
MIP Presolve eliminated 135 rows and 13 columns.
MIP Presolve added 15 rows and 15 columns.
Reduced MIP has 21 rows, 45 columns, and 105 nonzeros.
Reduced MIP has 30 binaries, 15 generals, 0 SOSs, and 0 indicators.
Presolve time = 0.08 sec. (0.10 ticks)
Probing time = 0.00 sec. (0.01 ticks)
Tried aggregator 1 time.
Reduced MIP has 21 rows, 45 columns, and 105 nonzeros.
Reduced MIP has 30 binaries, 15 generals, 0 SOSs, and 0 indicators.
Presolve time = 0.00 sec. (0.06 ticks)
Probing time = 0.00 sec. (0.01 ticks)
MIP emphasis: balance optimality and feasibility.
MIP search method: dynamic search.
Parallel mode: deterministic, using up to 4 threads.
Root relaxation solution time = 0.00 sec. (0.04 ticks)

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

      0     0    infeasible                                          5         

Root node processing (before b&c):
  Real time             =    0.09 sec. (0.46 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) =    0.09 sec. (0.46 ticks)

I am looking forward to hearing from you. thank you