Constraint declaration generates an error

Specific Domains Optimization (Mathematical)
1

Dear all,
how to type the constraint below in order to avoid an error.
for j in N1
if j>1 && j<7
@constraint(vrpm, sum(x[j,i,k] for i in N5, k in B if i!=j)
-sum(x[i,j,k] for i in N4, k in B, if i!=j) == 0)
end
end
If statement ( if j>1 && j<7) makes that error ( LoadError: MethodError: no method matching isless(::Int64, ::String))
Thanks,
Mamo

2

Please make it easier to help you by formatting your code and making it self-contained, e.g., here you don’t say what N1 is; see Please read: make it easier to help you.
From what I see, j is a String so I guess N1 contains some strings and then you try to compare it with 1 and 7. Strings cannot be compared to numbers hence the error.

2 Likes
3

yes, thanks blegat. N1 is the set of strings, by if statement j counter should exclude first and last member of the set N1.

4

Just do for j in N1[2:6] if you know that’s the range you’re after?

2 Likes
5

Thanks nilshg, two additional questions:
What is the command for printing the values of decision variables?
If I want to print the entire model print(model) but what if I want to see only a specific constraint in the derived form? I need to name it?

6

What is the command for printing the values of decision variables?

Use value

If I want to print the entire model print(model) but what if I want to see only a specific constraint in the derived form? I need to name it?

Not necessarily, you can also do con_ref = @constraint(...) and use con_ref to reference the constraint even if it has no name.

3 Likes
7

Thanks blegat!