How to make a if and else in alternative function in OPL?

Question

I want to make if the earn value is not same with the plan then choose alternative 2, if same then choose alternative 1. I used tuple mode to determine the 2 alternative in OPL using CP(constraint programming) I still stuck until this part

**subject to {
  forall (p in Precedences, m in Modes) {
 alternative(Tasks[p], all(m in Modes: m.taskId==p.id) mode[m]);**

thanks, I need this part to finish my master thesis, because I don't have a basic about programming

Answer 1

You can use presenceOf.

using CP;

int v=1;
// if v is 1 we choose a1p[1] , if not a1p[2];

dvar interval a1;
dvar interval a1p[i in 1..2] optional size i;

subject to {
  alternative(a1, a1p);
  (v==1) == (presenceOf(a1p[1])==1);
};

execute
{
  writeln(a1);
}

gives

<1 0 1 1>

but if I change v=1 to v=2 then I get

 <1 0 2 2>

Answer 2

thanks for response my question, I felt bless. this code plicable to using tuple? because I make my mode at tuple? when I tried using range 1..2 the dvar was error. this is my original code

tuple Mode {
  key int taskId;
  key int id;
  int pt;
  int costprod;
  int dmdIntRes [IntRes];
  int dmdExtRes [ExtRes];
}
{Mode} Modes = ...;

dvar interval Tasks [p in Precedences]in p.RelDate..EndMax   ; //in p.RelDate..EndMax in 0..EndMax
dvar interval mode[m in Modes] optional  size m.pt;

cumulFunction IntResUsage[r in IntRes] = 
  sum (m in Modes: m.dmdIntRes[r]>0) pulse(mode[m], m.dmdIntRes[r]);
  
cumulFunction ExtResUsage[r in ExtRes] = 
  sum (m in Modes: m.dmdExtRes[r]>0) pulse(mode[m], m.dmdExtRes[r]);
  
execute {
        cp.param.FailLimit = 10000;
}
 
minimize max(p in Precedences) endOf(Tasks[p]);
subject to {
  forall (p in Precedences, m in Modes) {
 
    alternative(Tasks[p], all(m in Modes: m.taskId==p.id) mode[m]);