  We study K-theoretic GLSM invariants with one-dimensional gauge group and
introduce elliptic central charges that depend on an elliptic cohomology class
called an elliptic brane and a choice of level structure. These central charges
have an integral representation related to an interpolation problem for the
elliptic brane and satisfy natural q-difference equations. Integral
representaions lead to the wall crossing statement for the central charges in
two different phases of the GLSM. We explain how the orbifold structure leads
to differences between wall crossing of the usual (K-theoretic) and elliptic
central charges.
