Originally posted by: wj1

Hi ,

forall(d in day,t in time,i in course: i ==2||i==19||i==41||i==43||i==45||i==47||i==58||i==60) sum(j in section) x[j][d][t]<=Nbr_IT_Labs; 

This constraint that means if section j assigned at day d at time t for all the d , t and courses that belong to IT courses (number of courses read frome xcel) should be inferior to nbr of IT labs

When i run this constraints it takes more than half an hour , without getting a result.

ANY HELP PLEASE !

When you say "run this constraints" do you mean solve a model containing them using CPLEX? When you say "without getting a result", do you meant that CPLEX fails to find a feasible solution, or that CPLEX finds a feasible solution but is unable to prove it is optimal?

I assume that there is more to the problem than just these constraints. Otherwise, CPLEX would immediately find a feasible solution (because x[j][d][t] = 0 for all j, d and t would be feasible). If CPLEX is taking a long time, it is almost certain other parts of the model are part of the reason.

Originally posted by: wj1

yes im solving a model using cplex because i had an infeasibility i started running constraint by constraint ...All constraints above that one give me a solution ...when i add that constraint , it's just c plex tke a long time to solve it now (more than 30 Minutes) and still waiting ...what do you think i should do ?

You did not answer my first question. When you say "more than 30 minutes", do you mean more than 30 minutes without finding a feasible solution, or more than 30 minutes with a feasible solution but with no proof of optimality (gap still too big)?