The ECL i PS e solver also stores each set variable in a data structure that increases linearly with the number of elements, so that the size of the problem as stored by ECL i PS e is also Θ(n 2 b); but the constant for ECL i PS e appears to be much smaller, and its search algorithm stores only incremental updates (with nodes per set instead of per element) on a stack as it explores the tree.
the ECL i PS e solver can process much larger instances than CPLEX without exhausting memory.