Constrains the variables and numbers in the collection Vars to integers in the eplex instance EplexInstance. If a variable in Vars is not already a problem variable for EplexInstance, it will be added as a new problem variable. The external solver will then take the integrality into account, i.e. solve a MIP/MIQP rather than a relaxed LP/QP problem.
Note that even when problem variables have been declared as integers in other solvers (ic or other external solver states), if the integrality constraint is not made known to this EplexInstance, any invocation of the eplex external solver (e.g. via eplex_solve/1) will only solve a continuous relaxation.