  We have considered a numerical scheme for the calculation of the equilibrium
properties of spin-1/2 XY chains. Within its frames it is necessary to solve in
the last resort only the 2N\times 2N eigenvalue and eigenvector problem but not
the 2^N\times 2^N one as for an arbitrary system consisting of N spins 1/2. To
illustrate the approach we have presented some new results. Namely, the xx
dynamic structure factor for the Ising model in transverse field, the density
of states for the isotropic chain with random intersite couplings and
transverse fields that linearly depend on the surrounding couplings, and the zz
dynamic structure factor for the Ising model in random transverse field. The
results obtained are hopped to be useful for an interpretation of observable
data for one-dimensional spin-1/2 XY substances.
