Hi,
That constraint would make the problem nonlinear (a bunch of products of
two variables). Hence, I really doubt you can do this in GLPK (where the
L stands for Linear).
However, the good news is that you might be able to reformulate your
constraint using some simple linearization technique.
Is it possible to set this constraint ?
SUM (Xi * Yj) = 1
where Xi and Yj are variables in {0,1}.
Your inequality can be written as follows:
sum zk = 1
where zk are binary variables such that zk = xi * yj (or,
equivalently, zk = xi yj). The latter constraints are still
non-linear,
