Originally posted by: GrauJack

I have this decision variable as

dvar float DemMax[1..12];

where each input is the maximum "Power Demand" for each month of the year (12 values).

 I need to use the maximum value and second largest value of that array on my objective function.

The largest value is no problem with

max(i in 1..12) DemMaxHP[i]

but I have not been able to get the second largest value.  

Any simple way for doing this?

I attach my code if helpful.

Thanks!

Hi,

you can use logical constraints.

Let me give you a tiny example:

dvar int x[1..5];

dvar int y; // biggest value
dvar int y2; // second biggest value
dvar int nby; // nb times biggest value

subject to
{
x[1]==2;
x[2]==3;
x[3]==2;
x[4]==3;
x[5]==1;

y==max(i in 1..5) x[i];
nby==sum(i in 1..5) (x[i]==y);
sum(i in 1..5) (x[i]==y2)>=1;  // y2 is one of the x
y2<=y-0.01;
sum(i in 1..5) (y2>=x[i])==5-nby;
}

which gives

y2=2

regards

PS : Many tricks at https://www.linkedin.com/pulse/how-opl-alex-fleischer/

Originally posted by: GrauJack

Thank you!, very simple and straightforward, I guess I need to study this language more 

Originally posted by: GrauJack

How would this change if I want the 2 highest values? (not necessarily the second largest) For example, if my values are [2,3,2,3,1] I need 3 and 3.

Hi,

why not trying

dvar int x[1..5];

dvar int y; // biggest value
dvar int y2; // second biggest value
dvar int nby; // nb times biggest value

subject to
{
x[1]==2;
x[2]==3;
x[3]==2;
x[4]==3;
x[5]==1;

y==max(i in 1..5) x[i];
nby==sum(i in 1..5) (x[i]==y);
sum(i in 1..5) (x[i]==y2)>=1;  // y2 is one of the x

(nby>=2) => (y2==y);
(nby==1) => y2<=y-0.01;
(nby==1) => (sum(i in 1..5) (y2>=x[i])==5-nby);
}

?

regards

https://www.linkedin.com/pulse/what-optimization-how-can-help-you-do-more-less-zoo-buses-fleischer/