Originally posted by: felycite28

Hello everyone ,

I have a mathematical model with the .mod ("trial.mod")extension and data file with the extension of .dat on cplex ; I want to import this model and the initial solution of it to the python to develop a sort of improvement heuristic which is based on the initial solution . To do that , I checked the prevoius examples of this forum and applied

main { 

thisOplModel.generate(); 

cplex.exportModel("trial.lp")

}

at the end of the .mod file. My python code is :

import cplex
import sys
def  sample(filename):
    c = cplex.Cplex("trial.lp")
    try:
        c.solve()
    except CplexSolverError:
        print ("Exception raised during solve")
    return
    status = c.solution.get_status()
    print ("Solution status = " , status, ":",)
    print (c.solution.status[status])
    print ("Objective value = " , c.solution.get_objective_value())

I have two questions :

1) When I run my python code I am getting "No module called 'cplex' error . What did I forget or what is my mistake , how can I correct my python code to reach the aim?

2) When i add the main block at the end of the .mod file , I run it and I got "No solution " for my mathemtical model , why ? I am asking to learn

P.S.I use Cplex 12.6

Thank you

Regards

Hi,

even before answering 1) and 2)

https://www.ibm.com/developerworks/community/forums/html/topic?id=0b6cacbe-4dda-4da9-9282-f527c3464f47

gives some options to call OPL from Python

1) Have you followed

https://www.ibm.com/support/knowledgecenter/SSSA5P_12.7.0/ilog.odms.cplex.help/CPLEX/GettingStarted/topics/set_up/Python_setup.html

?

2) With

main {
thisOplModel.generate();
cplex.exportModel("trial.lp");
}

you do not get any solution since you do not call solve and that is normal.

If you wrote

main {
thisOplModel.generate();
cplex.exportModel("trial.lp");
cplex.solve();
}

instead

then you would get a solution

NB: if you only need to generate a lp file you may use command line

oplrun -e trial.lp model.mod

regards

Originally posted by: felycite28

Hello Alex ,

I followed the directions you have said in 1) but I got the message of "cplex is compatible with python " message . I was using Python 3.5 (Cplex 12.6) and I removed Python 3.5 and downloaded Python 2.7 and tried to follow the same direction but again I am getting the same message . Is cplex compatible with both versions of python or not ? I am trying to understand if I did something wrong

Thank you in advance

Regards

Hi

In 12.7.1, this should work fine as can be read at

https://www.ibm.com/software/reports/compatibility/clarity-reports/report/html/softwareReqsForProduct?deliverableId=30B79120985B11E49CB249F9C96844EC&osPlatform=Windows

Can you move to CPLEX 12.7.1 ?

regards

Originally posted by: felycite28

I guess I solved it but I am not sure

I tried a few of IBM python examples they worked but since I need the primal solution of cplex  I inspired from your admipex6. py example ; anyway  and followed the code to do that on python :

import cplex
import sys
def sample1(filename):
    c=cplex.Cplex(filename)
    try:
        c.solve()
    except CplexSolverError:
        print "Exception raised during solve"
        return
    status=c.solution.get_status()
    print "Solution Status=", status,":",
    print c.solution.status[status]
    print "Objective value=",c.solution.get_objective_value()

but here , I still can not get the result ,objective value , I should connect with . mod and .dat but I could not achieve it .

Where I should indicate the name of the model and data to get solution ? (If it is filename part, I could not be sure about the extension of them and I am so newly learner , basically it is nightmare)

Thank you in advance

Regards

Hi,

take

dvar float+ Gas;
dvar float+ Chloride;

maximize
  40 * Gas + 50 * Chloride;
subject to {
  ctMaxTotal:     
    Gas + Chloride <= 50;
  ctMaxTotal2:    
    3 * Gas + 4 * Chloride <= 180;
  ctMaxChloride:  
    Chloride <= 40;
}

the obj you get in OPL is 2300

Then if you generate the lp file you get volsay.lp:

Maximize
 obj: 40 Gas + 50 Chloride
Subject To
 ctMaxTotal:    Gas + Chloride <= 50
 ctMaxTotal2:   3 Gas + 4 Chloride <= 180
 ctMaxChloride: Chloride <= 40
End

and then

import cplex
import sys
def sample1(filename):
    c=cplex.Cplex(filename)
    try:
        c.solve()
    except CplexSolverError:
        print ("Exception raised during solve")
        return
    status=c.solution.get_status()
    print ("Solution Status=", status),
    print (c.solution.status[status]);
    print ("Objective value=",c.solution.get_objective_value())

sample1("volsay.lp")   

gives

Tried aggregator 1 time.
LP Presolve eliminated 1 rows and 0 columns.
Reduced LP has 2 rows, 2 columns, and 4 nonzeros.
Presolve time = 0.02 sec. (0.00 ticks)

Iteration log . . .
Iteration:     1   Dual infeasibility =             2.500000
Iteration:     3   Dual objective     =          2300.000000
Solution Status= 1
optimal
Objective value= 2300.0
>>>

regards

Originally posted by: felycite28

tears of happiness ,

Million thanks  Alex,