Initialises the eplex instance EplexInstance. An eplex instance is an instance of the eplex solver, to which eplex linear arithmetic and integrality constraints can be posted, and to which an external LP/MIP solver can be associated and used to optimise the posted constraints with respect to some objective.
If EplexInstance is not an already existing eplex instance, a new eplex instance will be created and initialised. If it is an existing eplex instance, and it is not currently being used (having no outstanding posted constraints and no associated solver), it is effectively reinitialised. Otherwise, the predicate aborts with an error. Note that an eplex instance is a module, and each eplex instance can be associated with at most one solver at any time and vice versa. An eplex instance should NOT be erased (e.g. using erase_module/1), as this would only erase the module, but not the information that eplex keeps on it as an eplex instance.