In order to study the behavior of interior-point methods on very large
-scale linear programming problems, we consider the application of suc
h methods to continuous semi-infinite linear programming problems in b
oth primal and dual form. By considering different discretizations of
such problems we are led to a certain invariance property for (finite-
dimensional) interior-point methods. We find that while many methods a
re invariant, several, including all those with the currently best com
plexity bound, are not. We then devise natural extensions of invariant
methods to the semi-infinite case. Our motivation comes from our beli
ef that for a method to work well on large-scale linear programming pr
oblems, it should be effective on fine discretizations of a semi-infin
ite problem and it should have a natural extension to the limiting sem
i-infinite case.