Errors with operators

Hello @Melike , what do you intend to do by the constraint you wrote ? If you can tell me that, I can tell you the right way to model that constraint.

@Melike , do you mean - for all Stationen, the precedence relations must be satisfied ? s is an index in the Stationen set, correct ?

In the case, remove the Stationen* inside the sum and put s as the index domain of the constraint. Something like the screenshot below. This will be interpreted as "for all stations s, sum[j, Zourdnun...(j,s)] - sum[i, Zoutdnu...(i,s)] must be less than or equal to 0. (Ignore the colors of the text, see the highlighted s in the Index domain.. field)

@Melike , can you elaborate what does Stationnumber represents ?

Do you want to minimize the total number of stations used ?

Again, sum[(i,s),Stationen*Zuordnung_AufgabenStationen(I,s)] is incorrect. Stationen is a set, and you cannot multiply a set in a constraint or a variable.

If you want to sum Zuordnung_AufgabenStationen for only the last Task l, then something like below could work.

sum[(l,s)|l = last(SetTasks), Zuordnung_AufgabenStationen(l,s)]

My answer might not be what you are looking for because I don't have a proper understanding of your problem statement and how you have set up the different sets and variables, so sharing that would be helpful if you need more assistance.

I havent add the data yet and just now tried to add the data to the Tasks,but it didnt except it with the error "There is no operation defined for the operator = with arguments of data type numeric and data type element,arguments Number of Stations and last(Stations)". Aufgaben=Tasks .Stationsanzahl=Number of Stations. Zuordnung_AufgabenStationen=Assignment of tasks to Stations. Aufgabenzuordung= constraint for the task assignment. I send the picture for the variable Number of Stations and Tasks. j is the predecessortask.

@Melike , using Last(Stationen) as the definition for variable Stationenzahl is incorrect.

Last(Stationen) will return a set element. A variable of a math program must be a numerical quantity, not a set element.

If you want to minimize the number of stations used, I would recommend creating a binary variable bvStationUsed(s) which represents if a station is used or not. 1 = station in use, 0 = station not used.

Now, in your objective function use the definition sum[s, bvStationUsed(s)] which would give the total number of stations used.

You will also need an additional constraint restricting that a station can be assigned task only if that station is in use. So, something like

Constraint(i, s) with definition Zuordnung_AufgabenStationen(i, s) <= bvStationUsed(s)

(Assuming the i is an index in the set of tasks)