Originally posted by: Yasmine_Hal

Dear all,

After reading my problem in cplex and then optimizing it, when I want to display solution variables they are displayed but then cplex writes incumbent solution!!
So, what does it mean and why does it show??

Thanks in advance.
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Originally posted by: SystemAdmin

Could you please tell us what version and API of CPLEX you are using and could you please show us the exact output you are observing?
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Originally posted by: Yasmine_Hal

I had a problem with row c11: (Infeasibility row 'c11': 0 >= 1.) so I deleted the constraint from my problem and run it again through cplex. And when I did so, the problem was optimized but I get incumbent solution!!

I am using cplex interactive optimizer 11.2.0 .

This is the output (and I attached the problem if you would like to take a look at it):

Problem 'CPLEX_6000_UPDATED.txt' read.
Read time = 0.03 sec.
Tried aggregator 2 times.
MIP Presolve eliminated 12522 rows and 5567 columns.
MIP Presolve modified 10 coefficients.
Aggregator did 711 substitutions.
Reduced MIP has 84 rows, 92 columns, and 311 nonzeros.
Reduced MIP has 92 binaries, 0 generals, 0 SOSs, and 0 indicators.
Presolve time = 0.03 sec.
Clique table members: 48.
MIP emphasis: balance optimality and feasibility.
MIP search method: dynamic search.
Parallel mode: none, using 1 thread.
Root relaxation solution time = -0.00 sec.

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

• 0+ 0 2600.0000 0 ---

0 0 666.6667 18 2600.0000 666.6667 26 74.36%

• 0+ 0 680.0000 666.6667 26 1.96%

0 0 cutoff 680.0000 666.6667 26 1.96%

Solution pool: 2 solutions saved.

MIP - Integer optimal solution: Objective = 6.8000000000e+002
Solution time = 0.05 sec. Iterations = 26 Nodes = 0
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Originally posted by: Yasmine_Hal

Problem 'CPLEX_6000_UPDATED.txt' read.
Read time = 0.05 sec.
Tried aggregator 2 times.
MIP Presolve eliminated 12522 rows and 5567 columns.
MIP Presolve modified 10 coefficients.
Aggregator did 711 substitutions.
Reduced MIP has 84 rows, 92 columns, and 311 nonzeros.
Reduced MIP has 92 binaries, 0 generals, 0 SOSs, and 0 indicators.
Presolve time = 0.03 sec.
Clique table members: 48.
MIP emphasis: balance optimality and feasibility.
MIP search method: dynamic search.
Parallel mode: none, using 1 thread.
Root relaxation solution time = -0.00 sec.

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

• 0+ 0 2600.0000 0 ---

0 0 666.6667 18 2600.0000 666.6667 26 74.36%

• 0+ 0 680.0000 666.6667 26 1.96%

0 0 cutoff 680.0000 666.6667 26 1.96%

Solution pool: 2 solutions saved.

MIP - Integer optimal solution: Objective = 6.8000000000e+002
Solution time = 0.05 sec. Iterations = 26 Nodes = 0
Incumbent solution
Variable Name Solution Value
x2 1.000000
x3 1.000000
x9 1.000000
All other variables in the range 1-11 are 0.

Incumbent solution
Variable Name Solution Value
y2 1.000000
y9 1.000000
y10 1.000000
y12 1.000000
y13 1.000000
y20 1.000000
All other variables in the range 12-31 are 0.
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Originally posted by: SystemAdmin

I guess you are confused by the term "incumbent solution". During the search process CPLEX keeps around the best currently known feasible solution. This is called the current "incumbent solution". When a better solution is found, the incumbent is updated to be the new solution. When the solving process finishes, then the "incumbent solution" is an optimal solution of your problem. If the solving process is terminated prematurely (for example because of a time limit), then the "incumbent solution" is not necessarily optimal. It is just the best solution that CPLEX could find.
In any case, the "display solution var -" command that you are apparently using displays the "incumbent solution" to the screen. If the solving process finished, this is just an optimal solution.

Tobias
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Originally posted by: Yasmine_Hal

Dear Tobias,

I'm solving BS and RS allocation problem. The constraints written in the project are supposed to ensure for us 100% coverage for the area of interest, but after getting the solution from cplex I noticed that the area was not 100% covered -----> so the solution provided by cplex was not the optimal but still the best that cplex can find,, does it mean not all the constraints were satisfied??
Another thing, you said something about a time limit,, in the problem formulation I have nothing that indicates to having a specific running time,, so please can you elaborate more about what did you really mean? Is there something I can write in cplex to indicate that if the solving process finished or not??

Thanks a lot in advance.
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Originally posted by: SystemAdmin

The time limit is a parameter you can set to restrict the total run-time. For example, use

set time 3600

to restrict the run to one hour.

The incumbent solution will always be feasible, i.e., it should satisfy all constraints. It is not necessarily optimal, i.e., there might be a different feasible solution with better objective value. But if CPLEX finishes with an optimal status, then the incumbent is indeed optimal.

I don't understand your log output, actually. When I read in your problem, solve it, and display the solution using

read CPLEX_6000_UPDATED.lp
opt
display sol var -

then I get:

...
        Nodes                                         Cuts/ 
   Node  Left     Objective  IInf  Best Integer     Best Node    ItCnt     Gap
 
*     0+    0                         1560.0000                     26     --- 
*     0+    0                          680.0000                     26     --- 
      0     0      666.6667    10      680.0000      666.6667       26    1.96%
      0     0        cutoff            680.0000      666.6667       26    1.96%
Elapsed real time =   0.05 sec. (tree size =  0.00 MB, solutions = 2)          
 
Root node processing (before b&c):
  Real time             =    0.03 
Parallel b&c, 2 threads:          
  Real time             =    0.00 
  Sync time (average)   =    0.00 
  Wait time (average)   =    0.00 
                          ------- 
Total (root+branch&cut) =    0.03 sec.
 
Solution pool: 2 solutions saved.
 
MIP - Integer optimal solution:  Objective =  6.8000000000e+02
Solution time =    0.05 sec.  Iterations = 26  Nodes = 0      
 
CPLEX> disp sol var -
Incumbent solution   
Variable Name           Solution Value
x2                            1.000000
x3                            1.000000
x9                            1.000000
y2                            1.000000
y5                            1.000000
y8                            1.000000
y12                           1.000000
y13                           1.000000
y19                           1.000000
y21                           1.000000
y22                           1.000000
z12                           1.000000
z22                           1.000000
z32                           1.000000
z42                           1.000000
z59                           1.000000
z69                           1.000000
z79                           1.000000
z89                           1.000000
v82                           1.000000
v92                           1.000000
v102                          1.000000
z122                          1.000000
z132                          1.000000
z142                          1.000000
z152                          1.000000
z169                          1.000000
z179                          1.000000
z189                          1.000000
z199                          1.000000
v192                          1.000000
v1913                         1.000000
v202                          1.000000
v2013                         1.000000
v2113                         1.000000
v2213                         1.000000
z232                          1.000000
z242                          1.000000
z252                          1.000000
z262                          1.000000
z279                          1.000000
z289                          1.000000
z299                          1.000000
z309                          1.000000
v3013                         1.000000
v3113                         1.000000
v3213                         1.000000
v3313                         1.000000
z342                          1.000000
z352                          1.000000
z362                          1.000000
z372                          1.000000
z389                          1.000000
v3812                         1.000000
z399                          1.000000
v3912                         1.000000
z409                          1.000000
v4012                         1.000000
z419                          1.000000
v4113                         1.000000
v4213                         1.000000
v4313                         1.000000
v4413                         1.000000
v4522                         1.000000
v4622                         1.000000
v4722                         1.000000
v4812                         1.000000
v4912                         1.000000
z509                          1.000000
v5012                         1.000000
z519                          1.000000
v5112                         1.000000
v5212                         1.000000
v5313                         1.000000
v545                          1.000000
v5413                         1.000000
v555                          1.000000
v5513                         1.000000
v5622                         1.000000
v5722                         1.000000
v5822                         1.000000
v5912                         1.000000
v5922                         1.000000
v6012                         1.000000
v6112                         1.000000
v6212                         1.000000
v6312                         1.000000
v645                          1.000000
v655                          1.000000
v665                          1.000000
v6722                         1.000000
v6822                         1.000000
v6922                         1.000000
v7012                         1.000000
v7022                         1.000000
v7112                         1.000000
v7212                         1.000000
v7312                         1.000000
v7412                         1.000000
v755                          1.000000
v765                          1.000000
v775                          1.000000
v7822                         1.000000
v7922                         1.000000
v8021                         1.000000
v8022                         1.000000
v8121                         1.000000
v8212                         1.000000
v8312                         1.000000
v848                          1.000000
v8412                         1.000000
v858                          1.000000
v865                          1.000000
v875                          1.000000
v885                          1.000000
v8919                         1.000000
v9019                         1.000000
v9021                         1.000000
v9022                         1.000000
v9119                         1.000000
v9121                         1.000000
v9221                         1.000000
v9321                         1.000000
v948                          1.000000
v958                          1.000000
v968                          1.000000
z973                          1.000000
v978                          1.000000
z983                          1.000000
z993                          1.000000
v10019                        1.000000
v10119                        1.000000
v10121                        1.000000
v10219                        1.000000
v10221                        1.000000
v10319                        1.000000
v10321                        1.000000
v1048                         1.000000
v10421                        1.000000
v1058                         1.000000
v10521                        1.000000
v1068                         1.000000
z1073                         1.000000
v1078                         1.000000
z1083                         1.000000
v1088                         1.000000
z1093                         1.000000
z1103                         1.000000
v1115                         1.000000
v11119                        1.000000
v1125                         1.000000
v11219                        1.000000
v11221                        1.000000
v11319                        1.000000
v11321                        1.000000
v11419                        1.000000
v11421                        1.000000
v1158                         1.000000
v11521                        1.000000
v1168                         1.000000
v11621                        1.000000
v1178                         1.000000
z1183                         1.000000
v1188                         1.000000
z1193                         1.000000
z1203                         1.000000
z1213                         1.000000
w22                           1.000000
w52                           1.000000
w82                           1.000000
w122                          1.000000
w132                          1.000000
w192                          1.000000
w212                          1.000000
w222                          1.000000
All other variables in the range 1-6370 are 0.

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