Error 66 - equation symbol has no values assigned

GAMS
1

Hello,

I am having problems with my model. I’ve got two errors: the error 66 in the solve statement and the error 256 in the display statement (I know error 256 is consequential). On the listing file I get the following:

**** The following MIP errors were detected in model tdvrp:
**** 66 equation Eq4… symbol “tviag” has no values assigned
**** 66 equation Eq5… symbol “lsup” has no values assigned

Both these parameters come from gdx files, and the files are being generated without any issue, so I really don’t understand what is the problem. I will attach the model and the excel files (apparently it is not possible to add the gdx files).

Any help would be much appreciated, thanks in advance!
tviag.xlsx (17.8 KB)
lsup.xlsx (15.1 KB)
TDVRP.gms (2.2 KB)

2

That’s a good one and shows you that relaxed punctuation (e.g. do not require a ‘;’ where strict languages would require one) can bite you. You wrote

Parameters
tserv(i) tempo de servico em i/
1       300
...
11      0
/
lsup(i,j,m) limite superior do intervalo de tempo m para o arco ij
$call gdxxrw lsup.xlsx  par=lsup rng=lsup!A2 Rdim=3 Dset=i rng=lsup!A2 Rdim=1 Dset=j rng=lsup!B2 Rdim=1 Dset=m rng=lsup!C2 Rdim=1
$gdxin lsup.gdx
load lsup
$gdxin
cap(k) capacidade do veiculo k/ ...

(same with tviag) and you forgot that the compile time command to load data from a GDX file is **$**load, not load. Why did the GAMS compiler not complain? You are still in an open parameter declaration block (you did not terminate with a ‘;’) hence the compiler sees a symbol declaration of a symbol called load with symbol text lsup. You can confirm this by looking at the symbol table dump via $debug dmpsym:

  144                            tserv  PARAM   1    TRUE       7    TRUE   FALSE      TRUE      0   FALSE
  145                             lsup  PARAM   3    TRUE       0   FALSE   FALSE     FALSE      0   FALSE
  146                             load  PARAM   0   FALSE       0   FALSE   FALSE     FALSE      0   FALSE
  147                              cap  PARAM   1    TRUE       2    TRUE   FALSE      TRUE      0   FALSE

-Michael

3

Hi Michael,

Thank you very much for the answer, I can’t believe I missed that! I guess it’s because GAMS didn’t complain, as you mentioned. I have ran the model again, and that problem is solved. However, now when I run itl it says that equation 2 is infeasible, and terminates the execution:


**** Exec Error at line 129: Equation infeasible due to rhs value

**** INFEASIBLE EQUATIONS …

---- Eq2 =E= departure only occurs once for each client and starting depots

Eq2(1)… 0 =E= 1 ; (LHS = 0, INFES = 1 ****)

Eq2(2)… 0 =E= 1 ; (LHS = 0, INFES = 1 ****)

Eq2(3)… 0 =E= 1 ; (LHS = 0, INFES = 1 ****)

Eq2(4)… 0 =E= 1 ; (LHS = 0, INFES = 1 ****)

Eq2(5)… 0 =E= 1 ; (LHS = 0, INFES = 1 ****)

Eq2(6)… 0 =E= 1 ; (LHS = 0, INFES = 1 ****)

Eq2(7)… 0 =E= 1 ; (LHS = 0, INFES = 1 ****)

This model is a MILP formulation of a time dependent VRP, where the goal is to minimize the total time of all routes by choosing the best time interval m for each link (i,j). Basically, equations 1 and 2 define that each client is only visited once. I know this post should probably be in the modeling section, but since I started it here, I will continue it here. I will attach the model again because I added descriptions, so it is easier to understand it. If you could help me to figure out what is wrong with the formulation it would be great!

Once again, thank you very much for the reply,

Manuel
TDVRP.gms (3.11 KB)