  Using detailed exact results on pair-correlation functions of Z-invariant
Ising models, we can write and run algorithms of polynomial complexity to
obtain wavevector-dependent susceptibilities for a variety of Ising systems.
Reviewing recent work we compare various periodic and quasiperiodic models,
where the couplings and/or the lattice may be aperiodic, and where the Ising
couplings may be either ferromagnetic, or antiferromagnetic, or of mixed sign.
We present some of our results on the square-lattice fully-frustrated Ising
model. Finally, we make a few remarks on our recent works on the pentagrid
Ising model and on overlapping unit cells in three dimensions and how these
works can be utilized once more detailed results for pair correlations in,
e.g., the eight-vertex model or the chiral Potts model or even
three-dimensional Yang-Baxter integrable models become available.
