Performance MIP Relative Gap

Units:	-
Default Value:	0.0001
Validation Rule:	≥0
Description:	Declare the integer solution optimal when this gap is reached between the current integer solution and best-bound linear relaxation (this is not a measure of optimality).
Detail:

Performance MIP Relative Gap is a solver setting for the mixed integer optimizer. The parameter may take any value in the range 0.0 to 1.0.

When the value:

|bestbound-bestinteger|/(1e-10+|bestinteger|)

falls below the value of this parameter, the mixed integer optimization is stopped.

Here:

'bestinteger' refers to the objective function value associated with the best integer feasible solution found so far; and
'bestbound' refers to the objective function value of any linear relaxation to the integer problem that has yet to be 'ruled out' as potentially leading to a better integer solution

For example, to instruct the solver to stop as soon as it has found a feasible integer solution proved to be within half a percent of optimal, set the relative MIP gap tolerance to 0.5%. Note that this does not guarantee that the current integer solution is half a percent worse than optimal, it only says that the true optimal solution is no more than half a percent better than the current solution. Put another way, the solution at a gap of 0.5% might in fact be optimal, but the solver has yet to prove it so.

For unit commitment/economic dispatch problems a relative gap of between 0.1-1% can provide a good balance of quality and performance.