Hello :)
checkStuff() does not throw an error if I use direct indicator-based search (DIB) as infill criterion in a single-objective optimization. It only controls whether DIB is used in case of multi-criteria optimization, but not the other way around (cf. line 125 in checkStuff()). Instead an ugly error is thrown later, because diag() is called with nrow = -1 in line 276 of makeMBOInfillCritDIB. It would be nice if the input checking in checkStuff() also controls for wrong use of the multi-criteria infill function DIB.