In the modern formulation of lattice gauge-fixing, the gauge fixing condition
is written in terms of the minima or stationary points (collectively called
solutions) of a gauge-fixing functional. Due to the non-linearity of this
functional, it usually has many solutions called Gribov copies. The dependence
of the number of Gribov copies, n[U] on the different gauge orbits plays an
important role in constructing the Faddeev-Popov procedure and hence in
realising the BRST symmetry on the lattice. Here, we initiate a study of
counting n[U] for different orbits using three complimentary methods: 1.
analytical results in lower dimensions, and some lower bounds on n[U] in higher
dimensions, 2. the numerical polynomial homotopy continuation method, which
numerically finds all Gribov copies for a given orbit for small lattices, and
3. numerical minimisation ("brute force"), which finds many distinct Gribov
copies, but not necessarily all. Because n for the coset SU(N_c)/U(1) of an
SU(N_c) theory is orbit-independent, we concentrate on the residual compact
U(1) case in this article and establish that n is orbit-dependent for the
minimal lattice Landau gauge and orbit-independent for the absolute lattice
Landau gauge. We also observe that contrary to a previous claim, n is not
exponentially suppressed for the recently proposed stereographic lattice Landau
gauge compared to the naive gauge in more than one dimension.Comment: 39 pages, 15 eps figures. Published version: minor changes onl