  The success of models of coupled two-leg spin ladders in describing the
magnetic excitation spectrum of La_{2-x}Ba_xCuO_4 had been interpreted
previously as evidence for bond-centered stripes. In a recent article, however,
we have determined the magnetic coupling induced by the charge stripes between
bond- or site-centered spin stripes modeled by two- or three-leg ladders,
respectively. We found that only the site-centered models order. We further
indicated excellent agreement of a fully consistent analysis of coupled
three-leg ladders using a spin wave theory of bond with the experimental data.
Here, we provide a full and detailed account of this analysis.
