Suppose you would like to use a variable object (a C structure, or C++ class,
or Python class, etc) to represent a column in GLPK, it is probably natural to
let the variable object have an integer field called 'index', which is the
index of this variable in the GLPK model (the API of GLPK use this index very
often). But there is a problem: when you delete a variable, you must update all
this field for all variables behind the deleted variable. I am also aware of
another index, which is the name of each variable, but it is less efficient
(probably OK if doing Python). I wonder if there is a more elegant way to
implement a variable object that would significantly brings down the overhead
involved with variable deletions. Similar problem can be proposed for
constraints, of course, and I suspect the solution is similar too.