Gurobi's definition of MIPGap

[Austin]

Here's the definition of MIPGap used in Gurobi:

https://www.gurobi.com/documentation/7.0/refman/mipgap.html

It says that:

     gap = ( ObjBound - ObjVal ) / | ObjVal | 

where ObjBound and ObjVal are the MIP objective bound and incumbent solution objective, respectively. 

If the problem is of the minimization type, won't this give a negative gap? For example, if the best LB is 5 and the best UB (given by incumbent solution) is 10, it should say gap = ( 5 - 10 ) / |10| = - 0.5, or - 50%. 

However, Gurobi does not report a negative gap when I solve minimization problems. What am I missing?

Thanks,

Austin

[Tobias Achterberg]

This is a typo in the documentation. It should be the absolute value:

gap = | ObjBound - ObjVal | / | ObjVal |


Regards,

Tobias