- there was a confusion in gf imfreq, in the new case
where freq can be <0 (non real gf, or for product gf).
- index: is the matsubara n, as in the struct matsubara_freq
index can be >0 or <0
- linear_index : is the shift from the 0. It is always >0.
Fixed function to compute it.
- Also changed the construction of mesh_point in the generic iterator.
Before, was constructed with a mesh point of index 0
Now, added a new constructor on mesh_point_t, just taking the mesh
which construct the *first* mesh_point.
Fixed linear, discrete, product accordingly.
Added to the documentation of the concepts of gf.
- the arithmetics of the gf mesh_points :
the forwarding of the second argument was missing,
leading to subtle bugs e.g. in (in matrix case) :
deltaw(iom_) << iom_ * gw.singularity()(-1) + gw.singularity()(0) - gw(iom_);
because the partial evaluation of the expression introduced a dangling const matrix_view &
instead of moving the temporary matrix_view into the final matrix expression template.
