Originally posted by: pineapple365

I am trying to return a smallest integer array  in a constraint in CPLEX which uses the ceil() function, but keep getting the ''can not use dvar float in constraint''. Following is constraint:

 [CODE]

forall(i in Plants, h in Hubs, s in Ships)
        Nship[i][h] == plant_hub[i][h]/ShipCapa[s];
 forall(i in Plants, h in Hubs)
        N[i][h] = ceil(Nship[i][h]);

[/CODE]

The array is two-dimensional, but formulation is simple. I think ceil() function could be used in constraint, and there is something wrong with my coding.

Any help would be great.

Hi,

you cannot use ceil directly because it is not linear but you may write the following if you need to get

y=ceil(x)

within the constraints:

range r=1..4;

float x[r]=[1.5,4.0,2.0001,5.9999];

dvar int y[r];
dvar float f[r] in 0..0.9999999;

subject to
{
forall(i in r) y[i]==x[i]+f[i];

}

execute
{
writeln(x," ==> ",y);
}

assert forall(i in r) y[i]==ceil(x[i]);

which gives

[1.5 4 2.0001 5.9999] ==>  [2 4 3 6]

regards

Originally posted by: pineapple365

Alex, thank you for your kind explanation. I tried the way you said, and got the right answer! 

Regards.

pineapple