Originally posted by: xinzhangandy

Hello everyone, now I meet a problem when I caculate the objective value of a MIP model, I want to maxmize the workers needed to running a facility in all time period,  so I defined  a_k：average number of workers needed to handling per unit product at facility k, and b_kt: the product needed to produce at facility k in time period t  so the objective function should be: maximize sum(k in K, t in T)a[k]*b[k][t], since the number of workers needed in each time period should be an integer, so I want to use a ceil function to realize it ，but I do not know how to do, hope someone can help me, thank you

Hi

see

https://www.ibm.com/developerworks/community/forums/html/threadTopic?id=f203fd1f-cd1e-4a19-ba41-baeef24a29c6&ps=25

regards

Originally posted by: xinzhangandy

HI, thank you for the link, now I know how to realize ceil function in  constraints, but I think my problem is more complex. I hope the image I written in Word describe my problem clearly and can get help from you.

Hi,

in order to make sure an expression is integer you may also write a constraint such as this expression is equal to a dvar int.

Take

dvar float+ x;
dvar float+ y;

 

minimize abs(x-y);
subject to
{
x+y==5;
}

which divides 5 into 2.5 and 2.5

But then you need x to be integer.

Then you can write

dvar float+ x;
dvar float+ y;

dvar int intv;

minimize abs(x-y);
subject to
{
x+y==5;
x==intv;
}

regards

Originally posted by: xinzhangandy

Thank you very much, It is very nice of you to give me the idea of solving it.

Bests